WO2023217378A1

WO2023217378A1 - Process, plant and a stage of expansion for a plant for the production of boards and a board

Info

Publication number: WO2023217378A1
Application number: PCT/EP2022/062955
Authority: WO
Inventors: Gernot Von Haas
Original assignee: Dieffenbacher GmbH Maschinen- und Anlagenbau
Priority date: 2022-05-12
Filing date: 2022-05-12
Publication date: 2023-11-16

Abstract

The invention refers to a process, a plant for producing boards, a stage of expansion for existing plants plus a board out of raw material, especially palm fronds, wherein at least a part of the raw material is comminuted into a material (7) with a first shape and afterwards said material (7) is comminuted into a second shape which is usable as material for producing boards, subsequently said material is dried, eventually sieved into different fractions for different layers, mixed with a binder and subsequently spread with or without other materials as a mat onto a forming belt, wherein said mat is afterwards pressed into a board with a press. The invention is characterized in that before the reduction of the material (8) into its second shape the material (7) is suspended into a cleaning fluid (20), afterwards the material (7) and the contaminated liquid (17) are separated from each other before the cleaned material (8) is comminuted under atmospheric conditions into its second shape.

Description

PROCESS, PLANT AND A STAGE OF EXPANSION FOR A PLANT FOR THE PRODUCTION OF BOARDS AND A BOARD

The invention refers to a process and plant for the production of boards, especially based on strands out of palm fronds, according to the preamble of the claims 1 and 12.

Furthermore the invention refers to a board, especially based on strands out of palm fronds according to claim 19.

In the end the invention refers to a stage of expansion for a plant for the production of boards according to claim 22.

In the production of particleboards or fiberboards, there are used predominately flow able or free-flowing particles of differing sizes containing lignocellulose and/or cellulose, such as fibers, chips and the like. After having being provided with binder agents, these particles are discharged out of a dosing or metering hopper and delivered to a spreading head as a spreading apparatus, by means of a forming station. Through the spreading head, the particles, chips or fibers are spread to form a fleece or mat onto a continuously running forming belt, and are then formed to a finished panel in a subsequent pressing station.

As for reference it has to be mentioned that fiberboards usually are made out of debarked and chipped logs. The chips usually are distributed into water, compressed by a feeding screw sealing the following cooking area in which the chips are heated within a pressurized wet atmosphere and finally are fed to a refiner. The refinement of the wooden material into fibers by a refiner is a characterizing element of the production of fiber boards, e.g. MDF (medium density fiber boards), HDF (high density fiber boards). A common refiner consists out of two facing rotating discs with grooves and a distance small enough to disintegrate the material into fibers. The chips are fed into the center of the discs and are sent outwards due to the centrifugal force applied by the rotating discs. The material is within a pressurized atmosphere during the defibration process and let out into a so-called blowline via a steam valve for further processing, e.g. mixing with a binder, drying, spreading onto an endless forming belt and finally pressing into a board.

The use of palm leaves or palm fronds in the production of such engineered boards is just as well known in the state of the art. In particular the fronds of date palms, oil palms, sago palms, coconut palms, dwarf palms, fan palms, pinnate palms or the like, are used as the starting material. At some point the leaves are separated from the stems and mostly only the stems of the palm fronds are used. Usually the fronds respectively the stems are crushed into particles or chips, then heated and dried and in a subsequent process step be mixed with binder. After the mixing the material is spread onto an endless forming belt in one or more layers as a mat, eventually preheated and/or compacted and afterwards compressed and/or heated in a continuous press to form a line section, which is afterwards cut into individual boards. Of course the pressing may be also carried out in a single stroke press.

The production of oriented strand boards (OSB) or flake boards depends on in their direction adjustable flakes or strips and mostly by spreading different layers of these, especially with different orientations in the bordering layers. Producing such suitable flakes or strips needs usually well-proportioned natural wood, which is comminuted in a first step into chips with a certain length and are finally shaped in a knife ring flaker (German: Messerringzerspaner) into flakes with certain and usable dimensions for spreading them into a mat for pressing. In the following the first step of milling the material results in chips, the second step of comminuting the chips results in strands, despite the use of a knife ring flaker, as the word “strand” is used in the well-known “oriented strand boards”, which should be produced with this new process. Knife ring flakers usually comprises a knife ring and a set of counter blades for shredding the chips into strands. One or both of these system of knives/blades are moved for the production of strands. These strands are then dried, sorted in their dimension with sieves and used in their intended layer due to their dimensions. Usually after the drying process the strands are mixed with a binder and then spread onto the forming belt as soon as possible.

In certain areas of the world, usually near the equator suitable wooden resources for the production of boards, especially OSB-boards, are not existing in an sufficient amount or too expensive. Therefore it has been determined to use other materials such as palm fronds.

There is the need of defining the words and the possible use of certain parts of wood or palms in the board production process. The use of wooden material is described above and well known, even wooden branches can be used as raw material for the production of fibers or particles respectively such (particle or fiber) boards. Palms on the other hand have a tree-like form and are called palm trees.

Most palm trees have evergreen leaves, known as fronds, mostly at the top of an unbranched log, root or trunk. The large leaves or fronds have a stem with usual lateral appendages of leaflets or small leaves. So by moving up a tree trunk of a palm tree, there are fronds and therein stems with leaves. In the following the use of (palm) fronds is used for the cluster of stems with attached leaves. For producing boards mainly the stems are usable for the production of boards. Nevertheless at some point the leaves have to be separated from the stems.

All production methods of boards have mainly the disadvantage of costly efforts for disintegrating the raw material due to the wear regarding the knives. Furthermore due to the wear of the knives the maintaining of a constant quality of the produced material (strands) over time, especially by using knife ring flakers, is challenging. Both issues, cost efficient production vs. constant quality of the strands, are in conflict with each other.

The problems mentioned above should be addressed by the invention by creating a process and a plant for the production of boards, especially based on raw materials like recycled wood, annual plants and/or palm fronds.

Furthermore a board benefitting from the invention should be created as well as a stage of expansion for existing plants.

The problems are solved for the process, a plant for producing boards, a stage of expansion for existing plants plus a board by the features of the main claims.

Regarding the process the invention emanates of a process for the production of boards out of raw material, wherein at least a part of the raw material is comminuted into a material with a first shape and afterwards said material is comminuted into a second shape which is usable as material for producing boards, subsequently said material is dried, eventually sieved into different fractions for different layers, mixed with a binder and subsequently spread with or without other materials as a mat onto a forming belt, wherein said mat is afterwards pressed into a board with a press

The problem is solved by suspending the material into a cleaning fluid before it is reduced into its second shape, in which afterwards the material and the contaminated liquid are separated from each other before the cleaned material is comminuted under atmospheric conditions into its second shape.

The following advantages are obtained through the features of the invention: In the first using the inventive two-step comminution process including the cleaning process it is possible to reuse recycling material or inferior material in relation to fresh wood or tree trunks such as annual plants or palm fronds.

Secondary by using such material the risk of contaminants like sand, stones, dust, metals, or the like is obviously higher. As a fallout the wear in the second comminution machine e.g. at its knives is proportionally higher. By cleaning the material before it is flaked into the final shape from dust, silicates and other contaminants the wear is reduced significantly. Furthermore the running time of the second comminution device is much longer and the quality of the produced material with an optimal second shape is longer, too. Especially longer strands are produced with sharp knives, for example by using a knife ring flaker. Other means of production of suitable flakes or particles for the second or final shape are indeed possible and may be used for the cleaned material in the production of boards, e.g. by comminuting and integrating them into the production at one or more of the steps of drying, gluing, spreading, forming a mat.

The following features are combinable with the main idea of the invention and are able to improve the invention alone or in combination with other features furthermore.

According to another preferred aspect the material is positively-driven into or through the cleaning fluid, preferably mechanically, hydraulically and/or pneumatically mixed with the cleaning fluid. By using shearing forces applied into the suspension the clinging undesired materials are more easily separated from the material and are more easily separated with the liquid from the material in the next or following separation cycles.

During the suspension of the material in the cleaning fluid contaminants or undesired contaminants like sand, stones, dust, metals, or the like are staying in suspension whereas the cleaned material is separated from the contaminated liquid, preferably with at least one dewatering unit, which is arranged in and/or separately to the mixing unit.

In a further aspect of the invention the material is in suspension for about 5 to 240 seconds, preferably not more than 60 seconds, and is preferably dried pneumatically during or after the separation process. The longer time might be necessary to help the dissolution of the undesired particles from the material as well might help possible additives in the cleaning fluid to apply their effects to the material or the undesired particles. Additives might have degreasing, oiling, priming, smoothen or similar effects.

The cleaning fluid, the suspension and/or the contaminated liquid out of the suspension are cleansed by at least one separation, sedimentation or filtration process, preferably in the mixing unit, the dewatering unit, in the collecting tank and/or the cleaning unit, especially by extracting the undesired contaminants separated from the material. Such uses support the recycling of the cleaning fluid.

In another advantageous possibility the separation of the suspension into the cleaned material and the contaminated liquid the liquid might circulated and reused in a preferred embodiment as cleaning liquid for suspending the next amount of to be cleaned material, preferably with at least one cleaning unit directly connected to the mixing unit. In another preferred aspect the raw material might consist out of recycled wood, annual plants and/or palm fronds.

Additionally or alternatively the first shape of the material are chips with a certain length, preferably 90 mm to 180 mm, most preferably about 140 to 160 mm. These chips are easily disintegrated into strands to be oriented during the forming process of a mat.

Moreover the second shape of the material might be strands usable in the production of boards, preferably as orientated strands, most preferably with a thickness smaller than 1.1 mm or with a thickness about 0.7 mm.

Preferably the material or the chips are comminuted into the second shape with a knife ring flaker, especially into strands for a OSB production.

In a further aspect there might be additives added to the cleaning fluid. Preferably a cleaning liquid is used as a primer for the binder and/or has a degreasing effect. Using water as cleaning fluid is preferred.

For the separation of the cleaning liquid from the cleaned material an preferably ascending belt filter or an preferably ascending conveyor screw might be used. Furthermore the flow of cleaning liquid could be arranged in a countercurrent manner to the material during the process of separating.

A preferred embodiment might be that the cleaning fluid is poured in the mixing unit used with the incoming material as suspension and is separated as contaminated liquid from the cleaned material, at which the liquid is at least filtered into a liquid before reaching a collecting tank, preferably at which fine contaminants are sedimented, after what the liquid is recycled with a cleaning unit into the cleaning fluid and reused in the mixing unit once again. This arrangement might be a best practice solution for such process and a plant.

In the following the invention is discussed regarding a plant for the production of boards out of a raw material, wherein a first comminuting device is arranged for comminuting a raw material into a material with a first shape and a second comminuting device is arranged to comminute under atmospheric condition said material into a second shape usable as material for the production of boards in said plant, in which a dryer, eventually a screen, a mixing apparatus for applying binder to the material and subsequently a spreading apparatus for spreading the material onto an endless belt into a mat plus a press for pressing the mat into boards is arranged.

The inventive solution regarding such plant comprises a mixing device with a compartment at least filled with a cleaning fluid to some extent is arranged between the first and the second comminuting device to suspend the material into a cleaning fluid, at which in or after the mixing device a dewatering unit is arranged to separate the cleaned material from the contaminated liquid.

Preferably mechanical, hydraulic and/or pneumatic means to mix the material into the cleaning liquid and/or means for positively driving the material into the cleaning liquid are arranged in the mixing unit. Such might be a rotating paddle wheel or a static mixing unit for the flowing suspension.

Furthermore extracting means for suspended contaminants or undesired parts of the material out of the suspension and/or the cleaning liquid might be arranged in and/or after the mixing unit.

In a further aspect the cleaning fluid and after its suspension with the material the contaminated liquid are arranged in a circular flow, consisting at least of a mixing unit, a dewatering unit, a collecting tank and preferably a cleaning unit to cleanse the contaminated liquid into the cleaning liquid. Pumps and tubes for the connection of the separate parts of the plant should be arranged by an expert due to his experience and expertise.

Preferably a dewatering unit is arranged as belt filter and/or a conveyor screw with a porous mantle, preferably in an ascending manner. Turbulent flows during the separation process are preferred to strip undesired particles from the material.

In a preferred embodiment of the invention the circular flow of the cleaning fluid comprises in flow direction after the mixing unit and the dewatering unit for the suspension at least a filter for the contaminated liquid, a collecting tank for the filtered liquid and a cleaning unit for cleaning the liquid out of the collecting tank into a cleaning fluid for the mixing unit. In view of the pollution degree of the utilized material the steps of cleaning the contaminated liquid might be in- or decreased.

Additionally or alternatively the first comminuting device is suitable to disintegrate palm fronds or the stems of palm fronds, especially into a predetermined first shape. Regarding the second comminuting device a knife ring flaker is preferably arranged.

Last but not least a Board, especially an oriented strand board is created by an process according to the above mentioned features or is produced with a plant described earlier.

Especially due to the process or the plant the ratio of silicates is less than 0,3% in the board. Having said this can especially be determined after combustion of the board. The ratio of the different elements and the share of the silicates is then easily obtained. As the board might be consisting at least partially of palm stems of palm fronds which are used as material for the production of the board. In view of the ratio of silicates mentioned above, the ratio should be calculated according to the share of used material in the board which has been passed through the process or the plant mentioned. So to say if only 50 percent of the material has been derived of the silica content, after combustion the consisting ratio of silicates has to appropriately adjusted and calculated.

Another aspect of the invention is a stage of expansion for a plant for the production of boards as described above. Such inventive stage consists out of a mixing device with a compartment at least filled with a cleaning fluid to some extent is arranged between the first and the second comminuting device to suspend the material into a cleaning fluid, at which in or after the mixing device a dewatering unit is arranged to separate the cleaned material from the contaminated liquid.

Such stage can take further advantage of at least one feature of the method and plant described above and is especially used as a modular concept to enhance an existing plant.

The invention is described with the enclosed drawing and a practice example. In a plant (not shown completely in the drawing) and a process for the production of boards raw material is provided and disintegrated at least in a first comminution device, e.g. a chipper 11 or similar means. Such chippers are mostly very sturdy and produce chips with a certain length for further use. Usually oversized chips leaving the chipper are extracted from the material and are chipped or comminuted again. Hence these chips have a first shape, which is suitable for further processing and are usually further shredded in a second device to obtain their final shape, which is intended to be used for the production of boards. Most of the time material 8 with or without a final shape is dried in a drum dryer or belt dryer, eventually sieved into different fractions for different layers, mixed with a binder and subsequently spread with or without other materials as a mat onto a forming belt, whereas the mat is afterwards pressed into a board with a press.

The figure shows mainly the relevant and innovative part of a plant/process for producing boards, especially strand boards based on strands 21 , in which the at least once shredded material 7 is processed before the material is disintegrated in the second device, for example a knife ring flaker 9, to obtain the second or final useable shape of the material for producing the intended boards.

The material 7, after its first processing steps is reaching the part of the plant shown in the figure for cleaning the material 7 before it is processed as cleaned material 8 in a knife ring flaker 9. In the knife ring flaker 9, representing other usable comminuting means, the reduction of the material 8 into the second or final shape is made.

In the beginning of this part of the plant or the process part the material 7 is delivered after its chipping in a chipper 11 into a mixing unit 1 for mixing the material 7 with a cleaning fluid 20, for example water with or without additives is usable. In the mixing unit 1 means for agitating the suspension 16 out of cleaning fluid 20 and material 7 are arranged, for example a mechanical paddle wheel 10. Instead or in addition hydraulically or pneumatically mixing means are usable. Furthermore it is possible to guide the material in a positively manner through the cleaning fluid, especially comparable to a static mixer for fluid movements.

Due to the application of external forces into the suspension or by providing different velocities between the material 7 and the cleaning fluid 20 the cleaning effect is obtained or improved and impurities, contaminants, dust, sand or the like are solved into the suspension 16 as well and can be recovered out of the mixing unit 1 as sediments. For the sediments, moving down in the compartment of the mixing unit 1 a collector 12 is arranged, which is connected with the bottom of the compartment of the mixing unit 1 and is detachable from the compartment with the first valve 14. Usually, except for cleaning purposes of the compartment of the mixing unit 1 , the second valve 15 on the other end of the collector 12 is operated in an inverse manner as the first valve 14. Therefore the first valve 14 is open and the second valve 15 is closed to enable the collector 12 to receive the sedimentation out of the mixing unit. If the collector 12 is filled up the valves 14 and 15 are inversed and the collected sediments are fed to a dewatering unit 23 to recycle used fluid or to compact the sediments before they are delivered to a dump 2. To flush the collector 12 the valve 14 can be opened for a short time but under the risk of a carryover of material 7 into the collector. Preferably a cleaning is executed by pumping contaminated liquid out of a collecting tank 5 into the collector 12 without jetting in material 7.

The material 7 in suspension with the cleaning liquid 20 in the mixing unit 1 is transferred to a dewatering unit 3 as suspension 16. During the transportation a further cleaning effect of the material is to be expected and afterwards the cleaned material 8 is obtained by separating the contaminated liquid 17 from it.

Of course it is possible to obtain the cleaned material 8 out of the suspension in several steps, for example the mixing unit 1 may be suited to keep the main part of the cleaning fluid during the explication of the material 8. Usually the part of cleaning fluid moved to the dewatering unit 3 is only as much as to obtain a transporting function of the slurry, if the dewatering unit 3 is not integrated into the mixing unit 1 . It might be possible to use a belt filter, preferably with an ascending belt, for this separation. Nevertheless due to the transporting of the slurry or suspension 16 a further cleaning effect my occur and the dewatering process in the dewatering unit 3 leaves behind a contaminated cleaning fluid 17, which has to be cleaned preferably in a coarse filter 4 into a filtered but still slightly contaminated liquid 18. Several filter steps might be arranged before the circulated liquid 17, 18, 19 can be used as cleaning fluid 20 again. For example a sedimentation process can be arranged collecting tank 5, used as reservoir for the circulation. This tank 5 can as well be arranged as sedimentation unit, maybe with a similar collector used with the mixing unit 1.

As shown, the collecting tank 5 can be connected with a further cleaning unit 6, e.g. a hydro-cyclone, sieves or other separators as means for improving the quality of the contaminated and recycled liquid 19 into a cleaning fluid 20 before it is returned to the mixing unit 1.

The filter 4, the collecting tank 4 and other apparatuses of the plant might be connected to dewatering units 23 for compacting the undesired parts due to the cleaning of the material 7 into material 8 and might be connected with dumps 2 to deliver the undesired parts as collected and dried disposable waste or combustible material.

references: P1634WO mixing unit dump dewatering unit filter (coarse) collecting tank cleaning unit material (first shape) material (cleaned) knife ring f laker paddle wheel chipper collector valve 1 valve 2 suspension liquid (contaminated) liquid (contaminated, filtered) liquid (contaminated, recycle) fluid (cleaning) strands compartment dewatering unit

Claims

Claims Process for the production of boards out of raw material, wherein at least a part of the raw material is comminuted into a material (7) with a first shape and afterwards said material (7) is comminuted into a second shape which is usable as material for producing boards, subsequently said material is dried, eventually sieved into different fractions for different layers, mixed with a binder and subsequently spread with or without other materials as a mat onto a forming belt, wherein said mat is afterwards pressed into a board with a press, characterized in that before the reduction of the material (7) into its second shape the material (7) is suspended into a cleaning fluid (20), afterwards the material (7) and the contaminated liquid (17) are separated from each other before the cleaned material (8) is comminuted under atmospheric conditions into its second shape. Process according to claim 1 , characterized in that the material (7) is positively-driven into or through the cleaning fluid (20), preferably mechanically, hydraulically and/or pneumatically mixed with the cleaning fluid (20). Process according to any one of the preceding claims, characterized in that during the suspension of the material (7) in the cleaning fluid contaminants or undesired parts like sand, stones, dust, metals, or the like are staying in suspension whereas the (cleaned) material (8) is separated from the contaminated liquid, preferably with at least one dewatering unit (3), which is arranged in and/or separately to the mixing unit (1 ). Process according to any one of the preceding claims, characterized in that the material (7) is in suspension for about 5 to 240 seconds, preferably not more than 60 seconds, and is preferably dried pneumatically during or after the separation process. Process according to any one of the preceding claims, characterized in that the cleaning fluid (20), the suspension (16) and/or the contaminated liquid (17, 18, 19) are cleansed by at least one separation, sedimentation or filtration process, preferably in the mixing unit (1), the dewatering unit (3), in the collecting tank (5) and/or the cleaning unit (6), especially by extracting the undesired contaminants separated from the material (7). Process according to any one of the preceding claims, characterized in that after separation of the suspension (16) into the cleaned material (8) and the contaminated liquid (17) the liquid (17) is circulated and reused as cleaning liquid (20) for suspending the next amount of to be cleaned material (7), preferably with at least one cleaning unit (6) directly connected to the mixing unit (7). Process according to any one of the preceding claims, characterized in that the raw material (7) consists out of recycled wood, annual plants and/or palm fronds, and/or, that the first shape of the material are chips with a certain length, preferably 90 mm to 180 mm, most preferably about 140 to 160 mm, and/or that the second shape of the material (8) are strands usable in the production of boards, preferably with orientated strands, most preferably with a thickness smaller than 1.1 mm or with a thickness about 0.7 mm. Process according to any one of the preceding claims, characterized in that the material (8) or the chips are comminuted into the second shape, especially into strands (21 ), with a knife ring flaker (9). Process according to any one of the preceding claims, characterized in that a cleaning liquid with additives is used, preferably a cleaning liquid which is useable as a primer (for the binder) and/or has a degreasing effect, and most preferably water is used as cleaning fluid (20). Process according to any one of the preceding claims, characterized in that for the separation of the cleaning liquid (17) from the cleaned material (8) an preferably ascending belt filter or an preferably ascending conveyor screw is used, preferably the flow of cleaning liquid is used in a countercurrent manner to the material (7). Process according to any one of the preceding claims, characterized in that the cleaning fluid (20) is poured in the mixing unit (1 ), is used with the incoming material (7) as suspension (16), and is separated as contaminated liquid (17) from the cleaned material (8), at which the liquid (17) is at least filtered into a liquid (18) before reaching a collecting tank (5), preferably at which fine contaminants are sedimented, after what the liquid (18) is recycled with a cleaning unit (6) into the cleaning fluid (20) and reused in the mixing unit (1 ) once again. Plant for the production of boards out of a raw material, wherein a first comminuting device is arranged for comminuting a raw material into a material (7) with a first shape and a second comminuting device is arranged to comminute under atmospheric condition said material into a second shape usable as material for the production of boards in said plant, in which a dryer, eventually a screen, a mixing apparatus for applying binder to the material and subsequently a spreading apparatus for spreading the material onto an endless belt into a mat plus a press for pressing the mat into boards is arranged, characterized in that a mixing device (1 ) with a compartment (22) at least filled with a cleaning fluid (20) to some extent is arranged between the first and the second comminuting device to suspend the material (7) into a cleaning fluid (20), at which in or after the mixing device (1 ) a dewatering unit (3) is arranged to separate the cleaned material (8) from the contaminated liquid (17). Plant according to the claim before, characterized in that mechanical, hydraulic and/or pneumatic means to mix the material (7) into the cleaning liquid and/or means for positively driving the material (7) into the cleaning liquid are arranged in the mixing unit (1 ), e.g. a rotating paddle wheel (10) or a static mixing unit for the flowing suspension (16). Plant according to at least one of the preceding plant claims, characterized in that extracting means for suspended contaminants or undesired parts of the material (7) out of the suspension (16) and/or the cleaning liquid (17, 18, 19) are arranged in and/or after the mixing unit (1 ). Plant according to at least one of the preceding plant claims, characterized in that the cleaning fluid (20) and after its suspension with the material (7) the contaminated liquid (17, 18, 19) are arranged in a circular flow, consisting at least of a mixing unit (3), a dewatering unit (3), a collecting tank (5) and preferably a cleaning unit (6) to cleanse the contaminated liquid (17, 18, 19) into the cleaning liquid (20). Plant according to at least one of the preceding plant claims, characterized in that as dewatering unit (3) a belt filter and/or a conveyor screw with a porous mantle, preferably in an ascending manner, is arranged. Plant according to at least one of the preceding plant claims, characterized in that for the circular flow of the cleaning fluid (20) in flow direction after the mixing unit (1 ) and the dewatering unit (3) for the suspension (16) at least a filter (4) for the contaminated liquid (17), a collecting tank (5) for the filtered liquid (18) and a cleaning unit (6) for cleaning the liquid out of the collecting tank (5) into a cleaning fluid (20) for the mixing unit (1 ) are arranged. Plant according to at least one of the preceding plant claims, characterized in that the first comminuting device is suitable to disintegrate palm fronds or the stems from palm fronds, especially into a predetermined first shape and/or as second comminuting device a knife ring flaker (9) is arranged. Board, especially oriented strand board, produced by a process according to any claim of the claims 1 to 11 or produced with a plant according to any claim of the claims 12 to 18. Board according to claim 19, whereas the ratio of silicates is less than 0,3%, especially determined after combustion of the board. Board according to claim 19, whereas palm stems of palm fronds are used as material for the production of the board. Stage of expansion for a plant for the production of boards out of a raw material, wherein the plant a first comminuting device is arranged for comminuting a raw material into a material (7) with a first shape and a second comminuting device is arranged to comminute under atmospheric condition said material into a second shape usable as material for the production of boards in said plant, in which a dryer, eventually a screen, a mixing apparatus for applying binder to the material and subsequently a spreading apparatus for spreading the material onto an endless belt into a mat plus a press for pressing the mat into boards are arranged, characterized in that the stage consists out of a mixing device (1 ) with a compartment (22) at least filled with a cleaning fluid (20) to some extent is arranged between the first and the second comminuting device to suspend the material (7) into a cleaning fluid (20), at which in or after the mixing device (1 ) a dewatering unit (3) is arranged to separate the cleaned material (8) from the contaminated liquid (17). Stage of expansion according to claim 22, in what the features of one of the claims 13 to 18 are realized.