A system for mixing lignocellulosic fibers and a binding agent to be pressed into a fiberboard

Abstract

A system (1) for providing a fiberboard composition (60) comprising lignocellulosic fibers (61) and a binding agent (62). The system (1) comprises an application chamber (30), comprising a binding agent inlet (31). The application chamber (30) extends from a fiber passage (32) of the application chamber (30) arranged to direct incoming fibers (61) towards the binding agent inlet (31). The system (1) further comprises a blending tube (40), comprising a blending tube inlet (41) arranged inside the application chamber (30), for receiving fibers (61) and binding agent (62) from the application chamber (30). The blending tube (40) extends in a flow direction (FD) and the blending tube inlet (41) is arranged between the binding agent inlet (31) and the fiber passage (32) as seen in the flow direction (FD).

Description

[0001] A SYSTEM FOR MIXING LIGNOCELLULOSIC FIBERS AND A BINDING

[0002] AGENT TO BE PRESSED INTO A FIBERBOARD

[0003] Field of the invention

[0004] The present invention relates to a system for mixing lignocellulosic fibers and a binding agent to be pressed into a fiberboard. Further, it relates to a process for mixing lignocellulosic fibers and a binding agent to be pressed into a fiberboard

[0005] Background

[0006] Fiberboard is an engineered wood product that is made out of lignocellulosic fibers, most typically wood fibers. Wood fibers are pressed, typically with a binding agent (e.g. a urea-formaldehyde resin), to provide a fiberboard. Fiberboards, especially medium-density fiberboards (MDF), are used a lot in the furniture industry. Types of fiberboard in the art include medium-density fiberboard (MDF), and high-density fiberboard (HDF). For pieces of furniture that will be visible, a veneer of wood is often glued onto the fiberboard to give it the appearance of conventional wood. Further, the fiberboard may be provided with a foil, or it may be lacquered, to provide it with an esthetic outer surface. Fiberboards are typically produced from fresh wood.

[0007] The production of fiberboard could generally be held to incorporate provision of lignocellulosic fibers, optionally mixing the fibers with a binding agent, and pressing the resulting mixture into a fiberboard. The lignocellulosic fibers are generally formed from a material, like wood, comprising lignocellulosic fibers by refiner or de-fibrator machines. Further, lignocellulosic fibers may be provided by re-cycling fiberboards like HDF or MDF.

[0008] The required process conditions (e.g. high humidity, temperature and pressure) to generate fibers from pre-treated bigger particles or chips are provided by applying steam and pressure to the material in a process chamber. At the outlet of the process chamber, there will be a pressure drop and the outgoing material is accelerated; typically in a blow line. In the art, the binding agent has typically been applied at this stage, e.g. in the blow line, as mixing is convenient at this stage. However, this also implies that the binding agent is present when the fibers are dried. As recognized in the art, the drying condition to evaporate the residual moisture of the ligno-cellulosic fibers affects the performance of the adhesive system, i.e. binding agent, as the heat inevitable initiates curing reactions. This in turn calls for increased dosing of the binding agent, as well as the use of very slow curing adhesive systems. At the same time, it has some advantages to apply the binding agent to lignocellulosic fibers before drying them, as the moisture lowers the tendency of the agent to get stuck in the system and / or agglomerate the lignocellulosic fibers into fiber lumps.

[0009] Whereas attempts have been made in the art to overcome this, they typically suffer from severe formation of agglomerations at the application point.

[0010] In DEI 02006024895 Al a process for gluing fibers which involves passing a fiber-free air flow between a flow of hot air and fibers and an inner wall of a straight tube forming part of second dryer stage is disclosed. Such a process does however still suffer from some agglomerations in introducing the glued fibers into the process, as the fiber-free air flow does not fully prevent the binding agent from getting into contact with the inner wall of a straight tube. Further, there are no measures for preventing the glue from agglomerating when being applied to the fibers. The measures in DE102006024895A1 applies to a subsequent drying stage, i.e. a step of drying the glued fibers.

[0011] In DE10247414A1 a fiber gluing plant for making medium density fiberboard (MDF) having a fiber outlet tube with annular or off-circular cross section in region of spray jets is disclosed. Further, an air jacket may be present in between a fiber stream and a chute. Similarly to DEI 02006024895 Al, an air jacket does however not fully prevent the binding agent from contacting the inner wall and agglomerate.

[0012] DEI 632450 discloses a device for continuously mixing relatively small quantities of a finely divided component with a carrier material moved by a stream of air, in particular for wetting chip-like and fiber-like materials with binding agents. Such a system also suffers from agglomeration on the inner wall of a straight mixing tube. The mixing tube may be elastic such that agglomerations on the inner wall may be knocked off from outside.

[0013] It would be desired to provide an improved system and a related process for mixing lignocellulosic fibers, to be pressed into a fiberboard, with a binding agent.

[0014] Summary

[0015] According to a first aspect, a system for providing a fiberboard composition comprising lignocellulosic fibers and a binding agent is provided. The system comprises an application chamber comprising a binding agent inlet. The application chamber extends from a fiber passage of the application chamber. The fiber passage is arranged to direct incoming fibers towards the binding agent inlet. Via the fiber passage, the lignocellulosic fibers may be introduced into the application chamber. The fiber passage faces the binding agent inlet, whereby the incoming fibers may be directed towards the binding agent inlet. The application chamber extends from the fiber passage to the binding agent inlet. Further, the application chamber comprises a blending tube. In the blending tube, the lignocellulosic fibers and the binding agent are blended to deposit the binding agent on the lignocellulosic fibers. The binding agent is typically part of a liquid composition and it may be sprayed towards incoming lignocellulosic fibers by the binding agent inlet. In blending the lignocellulosic fibers and the binding agent, the liquid may be at least partly absorbed by the lignocellulosic fibers. The blending tube is used to remove the fiberboard composition from the application chamber in a flow direction, i.e. an outgoing flow of lignocellulosic fibers and a binding agent. The blending tube extends in the flow direction. Typically, the blending tube is straight. The blending tube comprises a blending tube inlet for receiving fibers and binding agent from the application chamber. The blending tube inlet is arranged inside the application chamber and in between the binding agent inlet and the fiber passage as seen in the flow direction. Further, the binding agent inlet is typically arranged on a central axis of the blending tube. Thus, the binding agent may be sprayed towards the blending tube inlet. Further, the system may comprise more than one binding agent inlet.

[0016] Examples of binding agents include MUF (melamine urea formaldehyde), MDI (methylene diphenyl isocyanate), and lignin (in addition to lignin comprised by the fibers). The binding agent is added to allow for binding the fibers together in pressing the fibers and the binding agent to provide the board. According to an embodiment, the binding agent is an isocyanate. The isocyanate may be methylene diphenyl diisocyanate (MDI), e.g. 4, 4'-methylene diphenyl di-isocyanate, or a polymethylene polyphenylene isocyanate, e.g. a polymethylene polyphenylene isocyanate comprising a residue of 4, 4'-methylene diphenyl di-isocyanate. According to such an embodiment, the amount of binding agent in a mix of lignocellulosic fibers and binding agent may be 1 to 10 wt%. Preferably, the amount of binding agent is 2 to 9 wt%; and more preferably 2.5 to 8 wt%. Further, the binding agent may be a bio-based system, such as bio-based wood adhesives based on any of the three major types of biopolymers: lignin, starch, and plant proteins. According to an embodiment, the binding agent is a ureaformaldehyde resin, or a melamine reinforced urea resin. Further, it may be a phenolformaldehyde resin. According to such an embodiment, the amount of binding agent in a mix of lignocellulosic fibers and binding agent may be 5 to 20 wt%. Preferably, the amount of binding agent in such a mix of lignocellulosic fibers and binding agent is 6 to 16 wt%. By arranging the system is this manner, the lignocellulosic fibers are directed in a first flow direction when entering the application chamber. The first flow direction is essentially parallel with longitudinal extension of the blending tube. Further, once entering the application chamber, the lignocellulosic fibers are turned towards the blending tube inlet into a second flow direction. The turning lignocellulosic fibers, as seen from the binding agent inlet in the second flow direction, may have the shape of a donut as seen from above. The second flow direction is typically essentially opposite to the first flow direction, i.e. the flow direction of the lignocellulosic fibers is shifted 160 to 200 degrees, such as about 180 degrees, in the application chamber. Further, as the binding agent inlet is arranged to direct the binding agent towards the turning lignocellulosic fibers and at least partly in the same direction as the second flow direction, the binding agent never gets in contact with an inner wall of the application chamber, as the lignocellulosic fibers flowing the first flow direction forms a barrier. Such a barrier is far more efficient than a separate airflow. This is advantageous, as the binding agent getting stuck in systems for providing fiberboard composition, is a common problem in the art. By arranging the system in this manner, such contamination may be reduced, or even avoided. Further, as the binding agent is directed towards the center of an outgoing flow of lignocellulosic fibers, also direct contact between the blending tube and the binding agent is minimized, at least in up-stream parts of the blending tube. As soon as the binding agent is brought in contact with the lignocellulosic fibers, the binding agent is adsorbed and / absorbed by the lignocellulosic fibers. Once adsorbed and / absorbed by the lignocellulosic fibers, the binding agent is less sticky and less prone to be stuck at inner walls of the system.

[0017] In order to optimize the flows within the application chamber and minimize the risk for any binding agent getting into contact with an inner wall of the system, the position of blending tube inlet within the application chamber is typically adjustable in the flow direction. By arranging the system such that the extension of the blending tube into the application chamber is typically adjustable, the position of blending tube inlet becomes adjustable. Further, the application chamber may be provided with one or more bypass air inlet(s). Such bypass air inlet(s) may assist in optimizing the flows within the application chamber and minimize the risk for any binding agent getting into contact with an inner wall of the system.

[0018] According to an embodiment, the blending tube inlet is tapered along the flow direction, i.e. the direction of the flow of the outgoing lignocellulosic fibers and binding agent. Thus, the blending tube inlet may be tapering from a wider dimension to a narrower dimension from its inlet end to its connection to the blending tube. Accordingly, the blending tube inlet may comprise an inlet opening and duct portion connecting the inlet opening to the blending tube. As already described, the duct portion may be tapered towards the blending tube. The blending tube inlet may thus have the shape of a funnel.

[0019] Further, the system is typically arranged such that a ring shaped nozzle is formed between the blending tube inlet and an inner wall of the application chamber. By forming such a nozzle, the lignocellulosic fibers are homogenously, and typically annularly, distributed in approaching the binding agent inlet and turning towards the blending tube inlet.

[0020] The binding agent inlet is typically a nozzle for spraying the binding agent onto the lignocellulosic fibers. Thus, the binding agent may be sprayed into the application chamber towards the blending tube inlet. Furthermore, the system may comprise more than one binding agent inlet in the form of a nozzle for spraying the binding agent onto the lignocellulosic fibers.

[0021] According to an embodiment, one or more air inlet(s) are arranged next to the binding agent inlet. A number of air inlets may be arranged around the binding agent inlet. The air inlet(s) are directed in a manner such that an airflow from the air inlet will guide the binding agent towards the blending tube inlet. Apart from guiding the binding agent, the air inlet(s) will also assist in preventing the binding agent from getting into contact with an inner wall of the application chamber before getting into contact with the lignocellulosic fibers. A number of air inlets may be arranged around the binding agent inlet. By arranging them in this manner, an annular airflow from the air inlets may enclose the binding agent in being directed towards the blending tube inlet. Further, the airflow from the air inlet(s) will assist in turning the incoming flow of lignocellulosic fibers towards the blending tube inlet.

[0022] As already described, the system is arranged in a manner, such that the lignocellulosic fibers are directed in a first flow direction when entering the application chamber. In the application chamber, the lignocellulosic fibers are turned towards the blending tube inlet into a second flow direction to exit the application chamber via the blending tube inlet. In order to assist a flow of fibers from the fiber passage to turn towards the blending tube inlet, a part of the application chamber facing the blending tube inlet may be vaulted. A part of the application chamber facing the blending tube inlet may thus be domed shaped, such as hemispherical or hemi- ellipsoidal. Further, the diameter of a cross-section of the application chamber, taken perpendicular to the flow direction, typically decreases in approaching the binding agent inlet.

[0023] According to an embodiment, the system further comprises a fiber inlet chamber that is connected to the fiber passage of the application chamber. The fiber inlet chamber at least partly encloses the blending tube. The fiber inlet chamber may be used to distribute the lignocellulosic fibers more evenly before entering the application chamber via the fiber passage.

[0024] A cross section of the fiber inlet chamber taken perpendicular to the flow direction is typically circular. Further, the fiber inlet chamber is typically provided with a fiber inlet. The fiber inlet is arranged to feed fibers into the fiber inlet chamber for further transport to the fiber passage. The fiber inlet is preferably arranged to feed the fibers at least partly tangentially into the fiber inlet chamber, whereby the fibers may flow along a spiral path around the blending tube inside the inlet chamber. To support this, the fiber inlet chamber may be arranged for making the fibers travel along a spiral path around the blending tube inside the inlet chamber. Thus, the fiber inlet chamber may be tapered to a smaller dimension when seen in a direction opposite to the flow direction. The fiber inlet chamber may thus have the form of a truncated cone.

[0025] In some embodiments, a diameter of a cross-section of the application chamber, taken perpendicular to the flow direction, increases from the fiber passage towards the position of the blending tube inlet. If the fiber inlet chamber is tapered to a smaller dimension when seen in a direction opposite to the flow direction, the fiber passage may form a throttle. In alternative embodiments, a diameter of a cross-section of the application chamber, taken perpendicular to the flow direction, may be essentially constant from the fiber passage towards the position of the blending tube inlet. Further, in yet further alternative embodiments, a diameter of a cross-section of the application chamber, taken perpendicular to the flow direction, may decrease from the fiber passage towards the position of the blending tube inlet.

[0026] According to an embodiment, the fiber inlet chamber is provided with an end plate at an end opposite to the connection to the fiber passage. The end plate may be planar and arranged perpendicular to the longitudinal extension of the fiber inlet chamber. Typically, the end plate is circular. In the end plate, a number of air inlets may be arranged, such as a number of slits. The air inlets may be arranged in a circle, such as in a number of concentric circles. Each air inlet may be arranged to let in air at least partly tangentially to the longitudinal extension of the fiber inlet chamber. The air inlet may be formed by punching or cutting the end plate to form air inlets and associated guiding tongues. Each guiding tongue may be a piece of material of the end plate being folded slightly inwards towards the connection to the fiber passage. Due to the folding of the material piece, the guiding tongue will form a type of baffle directing the air to flow in the direction set by the angle of the guiding tongue and the extension of the air inlet, such as slit.

[0027] In order to feed lignocellulosic fibers to the fiber inlet chamber via the fiber inlet, the system may further comprise a fan in flow communication with the fiber inlet of the fiber inlet chamber. The lignocellulosic fibers may be introduced into an air flow from the fan and carried by the air flow into the fiber inlet chamber.

[0028] Furthermore, the system is typically operated at sub-atmospheric pressure.

[0029] Operating the system at sub-atmospheric pressure, assist in turning the flow direction of the lignocellulosic fibers in the application chamber. In order to operate the system at sub-atmospheric pressure, the system may comprise a suction device, such as a pump, in flow communication with an outlet of the blending tube. The outlet of the blending tube is arranged at an end of the blending tube opposite to the blending tube inlet. The suction device is configured to draw the lignocellulosic fibers and the binding agent, once introduced into the application chamber, into the blending tube via the blending tube inlet. Furthermore, operating the system at sub-atmospheric pressure implies that air may be sucked into the system via air inlets, such as air inlet(s) arranged next to the binding agent inlet, and / or air inlet(s) arranged in the end plate of the fiber inlet chamber, and / or bypass air inlet(s).

[0030] In order to enrich lignocellulosic fiber in an airflow from the blending tube, the system may further comprise a separator, such as a cyclone. The separator may be arranged downstream or upstream, preferably downstream, of the suction device and in flow communication therewith. The separator is configured to at least partly separate a fiberboard composition comprising a mixture of the fibers and the binding agent from an airflow from the blending tube.

[0031] The temperature of the lignocellulosic fibers introduced into the application chamber is typically slightly higher than the ambient temperature, such as 30 to 60°C. In some embodiments, the temperature of the lignocellulosic fiber is higher than ambient temperature, such as 30 to 200°C, or such as 30 to 100°C. In order to condense some water in the blending tube and whereby lowering the tendency of the binding agent to form lumps as well as sticking to surfaces, the blending tube is provided with cooling means, such as a cooling jacket at least partly enclosing the blending tube along its longitudinal extension. The cooling jacket may be cooled by a fluid, such as water. According to an embodiment, the system further comprises a rotational drive connected to the blending tube, or to the cooling jacket if present. If connected to the cooling jacket, part of the inner blending tube may be static. The rotational drive is configured to rotate the blending tube, or the cooling jacket if present, along an axis being parallel with the flow direction. By rotating the blending tube, or to the cooling jacket if present, and especially the blending tube inlet, cleaning thereof is facilitated by e.g. scraper. The blending tube inlet may be connected to the cooling jacket if present such that they may rotate together. Further, the blending tube inlet may be provided with a cleaning device, such as a scraper. By arranging a cleaning device, such as a scraper, at the blending tube inlet, lignocellulosic fibers and / or binding agent getting stuck, e.g. in the form of agglomerated fiber lumps, may be scrapped of. By rotating the blending tube inlet, agglomerated fiber lumps may be removed by a stationary a cleaning device. Furthermore, the application chamber may comprises a waste outlet for taking out lumps, e.g. fiber lumps, removed from the blending tube inlet by the cleaning device.

[0032] In one embodiment, the rotational drive is configured to rotate at least the blending tube inlet, but typically the entire blending tube. If the cooling jacket is present, the rotational drive may be configured to rotate the cooling jacket together with at least the blending tube inlet.

[0033] According to a second aspect, there is provided a process of providing a fiberboard composition comprising lignocellulosic fibers and a binding agent. Such a composition may be used in the manufacture of fibers boards, e.g. medium density fiberboard, by pressing the composition into a board material. The process comprises the steps of:

[0034] - directing lignocellulosic fibers in a first flow direction;

[0035] - having the lignocellulosic fibers turning into a second flow direction; and

[0036] - directing a binding agent in the same direction as the second flow direction and towards the turning lignocellulosic fibers, to provide a stream comprising lignocellulosic fibers and binding agent. In turning into the second flow direction, the fiber are turning inwards, i.e. towards a center of a cross-section in the flow of lignocellulosic fibers taken perpendicular to the first flow direction. The second flow direction is at least 90° offset with respect to the first flow direction. Typically, the second flow direction is essentially opposite to the first flow direction, i.e. the flow direction of the lignocellulosic fibers is shifted 160 to 200 degrees, such as about 180 degrees, in turning the lignocellulosic fibers. As already described, directing a binding agent towards turning lignocellulosic fibers implies that lignocellulosic fibers flowing in the first flow direction will shield the binding agent from getting into contact with an inner wall of a system used in applying binding agent to lignocellulosic fibers. Further, the binding agent will typically be absorbed and / or absorbed lignocellulosic fibers before the shielding effect diminishes.

[0037] In order to enhance the shielding effect and provide steady flows, a crosssection in the flow of lignocellulosic fibers taken perpendicular to the first flow direction comprises a flow of lignocellulosic fibers being annular. In having turned into the second flow direction, the lignocellulosic fibers flow into the open center of the lignocellulosic fibers flowing in an annular manner in the first flow direction. Further, the binding agent may be directed towards the center of the annular flow of lignocellulosic fibers. The turning lignocellulosic fibers, as seen in the second flow direction, will have the shape of a donut as seen from above. Thus, the lignocellulosic fibers directed in the first flow direction may form an annular flow of lignocellulosic fibers. Further, in turning the lignocellulosic fibers into the second flow direction they may be directed inwards into an open center of the annular flow of lignocellulosic fibers.

[0038] According to an embodiment, the lignocellulosic fibers directed in the first flow direction form an annular flow before turning into the second flow direction. By having the lignocellulosic fibers forming an annular flow in the first flow direction, they may - once turned into the second flow direction - flow into an open center of the annular flow of lignocellulosic fibers flowing annularly in the first flow direction. Further, the binding agent may be directed towards the open center of the annular flow of lignocellulosic fibers, thereby preventing the binding agent from coming into contact with an inner wall of a system used in applying binding agent to lignocellulosic fibers.

[0039] According to an embodiment, the binding agent is guided by a separate airflow towards the turning lignocellulosic fibers. By guiding the binding agent with a separate airflow, the risk of the binding agent getting into contact with an inner wall of a system used in applying binding agent to lignocellulosic fibers is further lowered. The separate airflow guiding the binding agent may be an annular airflow enclosing the binding agent.

[0040] According to an embodiment, the lignocellulosic fibers flow in a spiral shaped flow before being directing into the first flow direction. By having the lignocellulosic flowing in a spiral shaped flow, the lignocellulosic fibers may be distribute more evenly before being directed in the first flow direction. In order to lower the tendency of the binding agent to form lumps, comprising binding agent, the process may further comprise a step of cooling the stream comprising lignocellulosic fibers and binding agent to condense water. Condensed water will create a protection layer on internal surfaces, whereby lowering or eliminating the tendency of the binding agent to stick to the internal surface. This is beneficial, as binding agent that sticks to the internal surfaces will cure and eventually be released to form spots in the material.

[0041] Brief description of the drawings

[0042] These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which:

[0043] In Fig. 1 a system for mixing lignocellulosic fibers and a binding agent to be pressed into a fiberboard, according to one embodiment, is shown;

[0044] In Fig. 2 an application chamber, according to one embodiment, of a system for mixing lignocellulosic fibers and a binding agent to be pressed into a fiberboard is shown. Further, a fiber inlet chamber according to one embodiment is shown;

[0045] In Fig. 3 an application chamber, according to one embodiment, of a system for mixing lignocellulosic fibers and a binding agent to be pressed into a fiberboard is shown. Further, a blending tube according to one embodiment is shown; and

[0046] In Fig. 4 the flows in a process of providing a fiberboard composition comprising lignocellulosic fibers and a binding agent, according to one embodiment, are schematically shown.

[0047] Detailed description

[0048] In Fig. 1, a system 1, according to one embodiment, for mixing lignocellulosic fibers 61 and a binding agent 62 to be pressed into a fiberboard is shown. The system 1 comprises an application chamber 30 comprising a binding agent inlet 31, and extending from a fiber passage 32. The binding agent inlet 31 and the fiber passage 32 are arranged at opposite ends of the application chamber 30. Thus, the fiber passage 32 is arranged to direct incoming fibers 61 towards the binding agent inlet 31. In the application chamber 30, the flow direction of the incoming fibers 61 is reversed, i.e. turned by around 180°, as indicated by the two arrows 61a. Further, the system 1 comprises a blending tube 40. The blending tube 40 is used to remove the fiberboard composition from the application chamber 30 in a flow direction FD. The blending tube 40 extends in the flow direction FD. In the blending tube 40, the lignocellulosic fibers 61 and the binding agent 62 are blended to deposit the binding agent 62 on the lignocellulosic fibers 61. The blending tube 40 comprises a blending tube inlet 41 arranged inside the application chamber 30 for receiving fibers 61 and binding agent 62 from the application chamber 30. The blending tube inlet 41 is arranged between the binding agent inlet 31 and the fiber passage 32, as seen in the flow direction FD. Further, the binding agent inlet 31 faces the blending tube inlet 41 and is arranged along a longitudinal axis of the blending tube 40.

[0049] Furthermore, a ring shaped nozzle 33 is formed between the blending tube inlet 41 and an inner wall 35 of the application chamber 30, as can been seen in the crosssection B-B in Fig. 1.

[0050] The blending tube inlet 41 is tapered along the flow direction FD, i.e. the blending tube inlet 41 tapers from a wider dimension to a more narrow dimension when moving from its inlet end to its connection to the blending tube 40. As shown in Fig. 1, the blending tube inlet 41 may have the shape of a funnel. Further, the extension of the blending tube 40 into the application chamber 30 is adjustable, whereby the position of the blending tube inlet 41 within the application chamber 30 is adjustable along the flow direction FD as indicated in the figures.

[0051] A part 30a of the application chamber 30 facing the blending tube inlet 41 is vaulted. As can be seen in Fig. 1, a vaulted part 30a may provided for by a crosssection, taken perpendicular to the flow direction FD, of the application chamber 30 decreasing in approaching the binding agent inlet 31. Such a cross-section is typically circular.

[0052] In the embodiment shown in Fig. 1, a diameter of a cross-section of the application chamber 30, taken perpendicular to the flow direction FD, increases from the fiber passage 32 towards the position of the blending tube inlet 41.

[0053] In order to operate the system at sub-atmospheric pressure, the system further comprises a suction device 43 in flow communication with an outlet 42 of the blending tube 40. The suction device 43 is configured to draw the fibers 61 and the binding agent 62 into the blending tube 40 via the blending tube inlet 41. Further, a separator 44, such as a cyclone, is arranged downstream of the suction device 43 and in flow communication therewith. The separator 44 is configured to at least partly separate a fiberboard composition 60 comprising a mixture of the fibers 61 and the binding agent 62 from an airflow 65 from the outlet 42 of the blending tube 40.

[0054] Additionally, the system comprises a fiber inlet chamber 20 that is connected to the fiber passage 32 of the application chamber 30. The fiber inlet chamber 20 at least partly encloses the blending tube 40. The fiber inlet chamber 20 is arranged along the longitudinal extension of the blending tube 40. The blending tube 40 extends from the application chamber 30 through the fiber inlet chamber 20. A cross section of the fiber inlet chamber 20 taken perpendicular to the flow direction (FD) is circular as shown in Section A-A in Fig. 1. A fiber inlet 21 of the fiber inlet chamber 20 is arranged to feed fibers 61 into the fiber inlet chamber 20 for further transport to the fiber passage 32. The fiber inlet 21 is arranged to feed the fibers 61 at least partly tangentially into the fiber inlet chamber 20. The fiber inlet chamber 20 is tapering to a smaller dimension when seen in a direction opposite to the flow direction FD. As shown in Fig. 1, the fiber inlet chamber 20 has the form of a truncated cone with the smaller end connected to the application chamber 30.

[0055] The system 1 further comprises a fan 23 in flow communication with the fiber inlet 21 of the fiber inlet chamber 20. A pipe 24 is arranged in between the fan 23 and the fiber inlet 21. The lignocellulosic fibers 61 may be fed into an airflow in the pipe 24. The lignocellulosic fibers 61 may be fed into an airflow in the pipe 24 by e.g. a rotary valve (not shown in Fig. 1). Further, the rotary valve could be arranged in combination with an injector (not shown in Fig. 1), e.g. a tongue, which guides the lignocellulosic fibers 61 into the airflow in the pipe 24 in the same direction as the airflow.

[0056] In Fig. 2 a part of a system 1 for mixing lignocellulosic fibers 61 and a binding agent 62 to be pressed into a fiberboard, according to one embodiment, is shown. Fig. 2 shows an embodiment, wherein the fiber inlet chamber 20 is provided with an end plate 25 at an end opposite to the connection to the fiber passage 32. A number of air inlets 26, such as slits, are arranged in the end plate 25. The air inlets 26 are arranged to let in air at least partly tangentially to the longitudinal extension of the fiber inlet chamber 20. Further, the air inlets 26 are arranged in a number of concentric circles, as shown in the view A-A in Fig. 2. The air inlets 26 are provided by associated guiding tongues 27, as can been seen in the enlargement of a cross-section the view A-A in Fig. 2. Each guiding tongue 27 is made by cutting or punching the material of the end plate 25 and slightly folding a piece of material of the end plate 25 inwards towards the connection to the fiber passage 32, in order to provide the inlet air with a tangential direction. Further, Fig. 2 shows an embodiment, wherein the system 1 further comprises a rotational drive 45 connected to the blending tube 40. The rotational drive 45 is configured to rotate the blending tube 40 about an axis being parallel with the flow direction (FD). Furthermore, the blending tube inlet 41 is provided with a cleaning device 47, such as scraper, for removing fiber lumps from the blending tube inlet 41. The application chamber 30 comprises a waste outlet 37 for taking out fiber lumps removed from the blending tube inlet 41 by the cleaning device 47.

[0057] In Fig. 3 a part of a system 1 for mixing lignocellulosic fibers 61 and a binding agent 62 to be pressed into a fiberboard, according to one embodiment, is shown. Fig. 3 shows an embodiment, wherein a number of air inlets 36 are arranged next to the binding agent inlet 31. The air inlets 36 are directed in a manner such that an air flow 63 from the air inlets 36 will guide the binding agent 62 towards the blending tube inlet 41. As can been seen in the Section A-A in Fig. 3, a cross-section of the airflow 63, taken perpendicular to its flow direction, is annular and encloses the binding agent 62. Further, the turning lignocellulosic fibers 61a enclose the airflow 63. The turning lignocellulosic fibers 61a, as seen from the binding agent inlet 31 in the flow direction FD, will have the shape of a donut as seen from above.

[0058] Further, Fig. 3 shows an embodiment, wherein the blending tube 40 is provided with a cooling jacket 48 at least partly enclosing the blending tube 40 along at least a portion of its longitudinal extension. In the embodiment shown, a rotational drive 45 is connected to the cooling jacket 48. The rotational drive 45 is configured to rotate the cooling jacket 48 about an axis being parallel with the flow direction FD. Further, the cooling jacket 48 is connected to the blending tube inlet 41 in a manner such that the blending tube inlet 41 also may rotate whereas the blending tube 40 is static. Furthermore, also the blending tube inlet 41 may be provided with cooling means (not shown in Fig. 3).

[0059] In Fig. 4, the flows in a process of providing a fiberboard composition 60 comprising lignocellulosic fibers 61 and a binding agent 62 are schematically shown. In the process, lignocellulosic fibers 61 are directed in a first flow direction FD1. The lignocellulosic fibers 61 are subsequently turned into a second flow direction FD2. The second flow direction FD2 is the same direction as the flow direction FD defined herein above. In Fig. 4, the second flow direction FD2 is opposite to the first flow direction FD1. Further, a binding agent 62 is directed in the same direction as the second flow direction FD2 and towards the turning lignocellulosic fibers 61a to provide a stream comprising lignocellulosic fibers 61 and binding agent 62. In the Section A-A in Fig. 4, taken perpendicular to the first flow direction FD1, an annular flow of lignocellulosic fibers 61 enclosing the binding agent 62 is shown. The binding agent 62 is directed towards the center of the annular flow of lignocellulosic fibers 61. The turning lignocellulosic fibers 61a, as seen in the second flow direction, will have the shape of a donut as seen from above.

[0060] Without further elaboration, it is believed that one skilled in the art may, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the disclosure in any way whatsoever.

[0061] Although the present invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and other embodiments than the specific embodiments described above are equally possible within the scope of these appended claims.

[0062] In the claims, the term "comprises / comprising" does not exclude the presence of other elements or steps. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous.

[0063] In addition, singular references do not exclude a plurality. The terms "a", "an",

[0064] “first”, “second” etc. do not preclude a plurality.

Claims

CLAIMS1. A system (1) for providing a fiberboard composition (60) comprising lignocellulosic fibers (61) and a binding agent (62), the system (1) comprising: an application chamber (30) comprising a binding agent inlet (31), wherein the application chamber (30) extends from a fiber passage (32) of the application chamber(30) arranged to direct incoming fibers (61) towards the binding agent inlet (31), and a blending tube (40) comprising a blending tube inlet (41) arranged inside the application chamber (30) for receiving fibers (61) and binding agent (62) from the application chamber (30), wherein the blending tube (40) extends in a flow direction (FD), and wherein the blending tube inlet (41) is arranged between the binding agent inlet(31) and the fiber passage (32) as seen in the flow direction (FD).

2. The system (1) according to claim 1, wherein the extension of the blending tube (40) into the application chamber (30) is adjustable, whereby the position of blending tube inlet (41) within the application chamber (30) is adjustable in the flow direction (FD).

3. The system (1) according to claim 1 or 2, wherein a ring shaped nozzle (33) is formed between the blending tube inlet (41) and an inner wall (35) of the application chamber (30); preferably the blending tube inlet (41) being tapered along the flow direction (FD), more preferably the blending tube inlet (41) tapering from a wider dimension to a more narrow dimension when moving from its inlet end to its connection to the blending tube (40).

4. The system (1) according to any one of claims 1 to 3, wherein at least one air inlet (36) is arranged next to the binding agent inlet (31), the air inlet (36) being directed in a manner such that an air flow (63) from the air inlet (36) will guide the binding agent (62) towards the blending tube inlet (41); and / or wherein the binding agent inlet (31) is a nozzle for spraying binding agent (62) onto the fibers (61).

5. The system (1) according to any one of claims 1 to 4, wherein a part of the application chamber (30) facing the blending tube inlet (41) is vaulted, wherebyassisting a flow of fibers (61a) from the fiber passage (32) to turn towards the blending tube inlet (41).

6. The system (1) according to any one of claims 1 to 5, wherein the system (1) further comprises a fiber inlet chamber (20) that is connected to the fiber passage (32) of the application chamber (30), wherein the fiber inlet chamber (20) at least partly encloses the blending tube (40).

7. The system (1) according to claim 6, wherein a cross section of the fiber inlet chamber (20) taken perpendicular to the flow direction (FD) is circular, and wherein a fiber inlet (21) of the fiber inlet chamber (20) is arranged to feed fibers (61) into the fiber inlet chamber (20) for further transport to the fiber passage (32); preferably the fiber inlet (21) is arranged to feed the fibers (61) at least partially tangentially into the fiber inlet chamber (20), preferably the fiber inlet chamber (20) is arranged for making the fibers flow along a spiral path around the blending tube (40) inside the inlet chamber (20).

8. The system (1) according to claim 6 or 7, wherein the fiber inlet chamber (20) is provided with an end plate (25) at an end opposite to the connection to the fiber passage (32), wherein a number of air inlets (26) are arranged in the end plate (25), preferably the air inlets (26) being arranged to let in air at least partly tangentially to the longitudinal extension of the fiber inlet chamber (20).

9. The system (1) according to any one of claims 6 to 8, wherein the fiber inlet chamber (20) is tapering to a smaller dimension when seen in a direction opposite to the flow direction (FD).

10. The system (1) according to any one of claims 7 to 9, wherein the system (1) further comprises a fan (23) in flow communication with the fiber inlet (21) of the fiber inlet chamber (20).

11. The system (1) according to anyone of claims 1 to 10, wherein a suction device (43) is in flow communication with an outlet (42) of the blending tube (40), wherein the suction device (43) is configured to draw the fibers (61) and the binding agent (62) into the blending tube (40) via the blending tube inlet (41).

12. The system (1) according to claim 11, wherein the system (1) further comprises a separator (44), such as a cyclone, arranged downstream or upstream, preferably downstream, of the suction device (43) and in flow communication therewith, wherein the separator (44) is configured to at least partly separate a fiberboard composition (60) comprising a mixture of the fibers (61) and the binding agent (62) from an airflow (65) from the outlet (42) of the blending tube (40).

13. The system (1) according to claim anyone of claims 1 to 12, wherein the blending tube (40) is provided with cooling means, such as a cooling jacket (48) at least partly enclosing the blending tube (40) along at least a portion of its longitudinal extension.

14. The system (1) according to anyone of claims 1 to 13, further comprising a rotational drive (45) connected to the blending tube (40), wherein the rotational drive (45) is configured to rotate the blending tube (40) about an axis being parallel with the flow direction (FD).

15. The system (1) according to anyone of claims 1 to 14, wherein the blending tube inlet (41) is provided with a cleaning device (47), and wherein the application chamber (30) comprises a waste outlet (37) for taking out lumps removed from the blending tube inlet (41) by the cleaning device (47).

16. A process of providing a fiberboard composition (60) comprising lignocellulosic fibers (61) and a binding agent (62), the process comprising the steps of:- directing lignocellulosic fibers (61) in a first flow direction (FD1);- having the lignocellulosic fibers (61) turning into a second flow direction (FD2), the second flow direction (FD2) being at least 90 degrees offset with respect to the first flow direction (FD1);- directing a binding agent (62) in the same direction as the second flow direction (FD2) and towards the turning lignocellulosic fibers (61a), to provide a stream comprising lignocellulosic fibers (61) and binding agent (62).

17. The process of providing a fiberboard composition (60) according to claim16, wherein the lignocellulosic fibers (61) directed in the first flow direction (FD1) forman annular flow of lignocellulosic fibers (61) before turning into the second flow direction (FD2).

18. The process of providing a fiberboard composition (60) according to claim 17, wherein the lignocellulosic fibers (61), in turning the lignocellulosic fibers (61) into the second flow direction (FD2), are directed inwards into a center of the annular flow of lignocellulosic fibers (61) in the first flow direction (FD1).

19. The process of providing a fiberboard composition (60) according to any one of claims 17 to 19, wherein the binding agent (62) is directed towards the center of said annular flow of lignocellulosic fibers (61) in the first flow direction (FD1).

20. The process of providing a fiberboard composition (60) according to any one of claims 16 to 19, wherein the second flow direction (FD2) is essentially opposite to the first flow direction (FD1).

21. The process of providing a fiberboard composition (60) according to any one of claims 16 to 20, wherein a cross-section taken perpendicular to the first flow direction (FD1) comprises a flow of lignocellulosic fibers (61) being annular.

22. The process of providing a fiberboard composition (60) according to claim 21, wherein the binding agent (62) is directed towards the center of the annular flow of lignocellulosic fibers (61).

23. The process of providing a fiberboard composition (60) according to any one of claims 16 to 22, wherein the binding agent (62) is guided by a separate airflow (63) towards the turning lignocellulosic fibers (61a).

24. The process of providing a fiberboard composition (60) according to any of claims 16 to 23, wherein the lignocellulosic fibers (61) flow in a spiral shaped flow when being directed into the first flow direction (FD1).

25. The process of providing a fiberboard composition (60) according to any one of claims 16 to 24, wherein the process further comprises the step of:- cooling the stream comprising lignocellulosic fibers (61) and binding agent (62) to condense water.

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