Process for producing fiberboard with reduced VOC emissions.

Abstract

The present invention relates to a process for producing fiberboard having reduced VOC emissions.

Description

[Technical field]

[0001] The present invention relates to a process for producing fibreboard, in particular HDF or MDF board, having reduced VOC emissions. [Background technology]

[0002] Continuous processes for the production of wood fibres based on lignocellulosic materials such as wood, straw or bagasse using dry and wet techniques include, but are not limited to, the grinding of the raw materials into loose fibres or fibre aggregates which in subsequent steps are coated with adhesives, dried, moulded and pressed into the final product, the so-called board or fibreboard. Nowadays, the disaggregation of fibres from the raw materials is preferably carried out in a so-called thermomechanical process in a single step or in a thermal and mechanical process in at least two separate steps.

[0003] Before the first heat treatment, the wood chips are usually washed to remove impurities such as mud or stones. The thermal treatment, i.e. the heating of the raw material, is carried out, for example, in a first heat treatment device, in particular at atmospheric pressure, at a preferred temperature of up to about 100 degrees Celsius, followed by a second heat treatment device, preferably pressurized, in particular at a pressure of about 4-13 bar, for example at a temperature of approximately 150-190 degrees Celsius. The residence time of the wood chips in the heat treatment device can be adjusted depending on the prevailing process conditions and may be, for example, between about 1 and 10 minutes. According to the related art, the thermal heating in the second heat treatment device is preferably carried out with steam. Mechanical processing is then carried out in a refiner, also called a fiberizer. The residence time of the wood chip raw material in the refiner is short. The energy converted into mechanical energy in connection with the mechanical processing is transformed into heat in the size reduction zone in the processing system and appears as steam generated from the exhaust gases, in particular from the moisture in the raw material.

[0004] After defibration in the refiner, the wood fibres are usually conveyed by air pressure to a fibre dryer where the drying process is carried out with a large volume of air and a controlled inlet temperature of about 140-200 degrees Celsius, depending on the moisture content of the fibres at that time. The fibres are mechanically separated from the drying wind. The dried fibres are then conveyed further, moulded, pre-pressed and final pressed into boards. The drying wind is subjected to exhaust gas cleaning. For this, wet cleaning, wet electrofilters or biofilters and biological wastewater treatment are used.

[0005] According to the related art, the wood emissions released during the de-fibering and drying, especially in the second heat treatment unit, together with the fibrous bulk material, are conveyed from the first heat treatment unit through a refiner to a dryer, where they are largely separated from the fibers, and finally, the moist dry air from the dryer is sent to the atmosphere after exhaust gas cleaning. These wood emissions mainly contain volatile organic substances, so-called volatile organic compounds (VOCs).

[0006] Among the VOCs, there are substances whose solubility in water is so low that in the cleaning of moist exhaust gases their degree of separation is only a few percent, or even close to zero. This is especially true for terpenes. For that reason, wet separation processes are known to only achieve an emission reduction of 10-30%. The low solubility is due to the substance's inherently low solubility in water as well as the strong dilution in dry air, which drastically reduces the partial pressure and therefore the thermodynamic driving force. Terpenes are derived from the resins of the wood used. Terpenes are volatile oils. Terpenes are also called turpentine.

[0007] The remaining amount that is not discharged from the dryer is sent along the fiber stream to subsequent process units and subsequently discharged into the surrounding atmosphere or appears as a by-product in the final board product. Thus, emissions into the atmosphere can also occur from the final product.

[0008] From WO 1999 / 10594 it is already known that the second heat treatment device is provided with an upper outlet for degassing the organic effluents discharged therein. Here, steam is introduced into the lower part of the first heat treatment device, and the wood chips entering the upper part of the first heat treatment device are washed in the counterflowing steam during the condensation of the steam. This is achieved by the steam moving upwards through the wood chip column to the cooler wood chips in the upper part of the first heat treatment device. The discharged effluents, exhaust air and steam, which arise from the evaporation of moisture in the wood chips, are separated and discarded from the outlets in the corresponding devices. This publication also reveals that the wood chips from the first heat treatment device are conveyed to a refiner by means of a screw conveyor, which compresses and dewaters the wood chips during the conveyance.

[0009] From EP 1 597 427 A1 it is known how the exhaust gases generated during compression are discharged in a screw conveyor via an outlet located in the compression zone. The plant according to this document is characterized in that an exhaust gas outlet is located in the compression zone for dissipating the evaporated water that is generated during compression of the wood chips and contains the VOC-containing exhaust gases.

[0010] EP 2573258 A1 describes a method and an apparatus for processing wood chips for the production of wood-containing fibrous materials. With regard to washing the wood chips, it is mentioned that this is done by heating to about 90°C using water heated to 98°C.

[0011] US Pat. No. 4,925,527 describes a method for recovering turpentine in a thermal mechanical pulp (TMP) process in which an air stream is taken from a refiner and fed to a condenser.

[0012] EP 1021612 A1 describes a plant for producing and processing wood fibres, comprising a fibre production section with a wood chip preheater and a beater, the function of which is to loosen the fibres from the wood chips, and at least one dryer stage, the function of which is to dry the fibres. Between the fibre production section and the dryer stage, a steam separator section is provided, which includes a cyclone separator, the inlet of which is connected to a blower line used for the fibres and steam obtained from the beater machine. The lower outlet of the cyclone separator is connected to a fibre conveying / drying line via a lock gate. The upper outlet of the cyclone separator is connected to a device, the function of which is to separate volatile organic substances from the steam of the cyclone separator and to recover heat.

[0013] US 2012 / 227918 A1 describes a refiner steam separation system that includes a blowline for conveying a fibrous material mixture from a refiner to an inlet of a steam separator. Exhaust steam is dissipated from the separator through an exhaust steam outlet. The cleaned fibrous material is dissipated from the separator through an outlet, thereby preventing a significant portion of the exhaust steam from reaching the outlet. A transfer tube is connected to the outlet and a dryer duct to convey the cleaned fibrous material between the two. A resin inlet is connected to the transfer tube and supplies resin to the transfer tube. After the resin is mixed with the cleaned fibrous material, the cleaned fibrous material is dried in the dryer duct. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 1999 / 10594 [Patent Document 2] European Patent Application Publication No. 1597427 [Patent Document 3] European Patent Application Publication No. 2573258 [Patent Document 4] U.S. Pat. No. 4,925,527 [Patent Document 5] European Patent Application Publication No. 1021612 [Patent Document 6] US Patent Application Publication No. 2012 / 227918 Summary of the Invention [Problem to be solved by the invention]

[0015] However, for environmentally friendly wood processing, there is a need to remove VOCs even more efficiently from processes for producing fiberboards, in particular HDF or MDF boards, which should also enable a resource-saving process. [Means for solving the problem]

[0016] According to the invention the solution to the problem is achieved by a process for producing fibreboard with reduced VOC emissions having the features set out in claim 1. Preferred configurations of the invention are set out in the dependent claims and in the following specification, each of which may represent an aspect of the invention individually or in combination.

[0017] 1. A process for producing fiberboard having reduced VOC emissions, comprising: a) providing wood chips containing wood; b) heat treating the wood chips in a heat treatment device or devices; c) Crushing, in particular defibrating, the wood chips in a refiner; d) bonding the crushed, in particular defibrated, wood chips; e) compressing the crushed, in particular defibrated and glued wood chips to form a fibreboard; At least f) A process is described in which steam used or resulting from the process is separated in a controlled manner, in particular continuously, from the process at at least one steam discharge location, in a predetermined amount range such that the lower and upper limits of the amount range of the total separated steam depend on at least one specification of the wood chips used in step a).

[0018] Such a process allows for a particularly advantageous way of efficiently reducing environmentally harmful VOC emissions in the manufacture of fiberboard. Moreover, a resource-saving process is possible.

[0019] The term VOC (volatile organic compounds) within the meaning of the present invention refers in particular to volatile compounds present in the wood used as raw material for the process described herein. In particular, the VOCs described in this process are terpenes, which are present in the wood as wood oils. By way of example, the following substances may be mentioned, which may be present in the weight percentages indicated in brackets based on the VOCs contained: α-pinene (20-70%), β-pinene (5-20%), limonene (1-5%), camphene (1-5%), phenol (0.2-2%). Further components may include myrcene, α-, β-phellandrene, 3-carene, cymene, terpinol, ocimene.

[0020] The term "controlled" within the meaning of the present invention means that, in terms of the separation of steam, the amount of steam and / or the material flow to be separated is adjustable, preferably controllable. In this respect, non-adjustable and / or non-controllable steam discharge positions are not to be understood as controlled steam separation within the meaning of the present invention.

[0021] The process described herein is used to manufacture fibreboards. A fibreboard within the meaning of the present invention is understood to be a board having wood fibres in a matrix containing a binder, as is generally known. For example, fibreboards may be so-called medium density fibreboards (e.g. 700-800 kg / m3 300 kg / m3) or low density fibreboards (for example LDF having a density of less than 650 kg / m3). Furthermore, so-called high density fibreboards (for example 800 kg / m3) may also be used. 3 More preferably, MDF boards or HDF boards may be produced using the described process. Such fiberboards are particularly suitable for indoor construction as under-roof boards or for exterior cladding of walls. These boards are also widely used in furniture manufacturing. They are also suitable for application in the interior fittings of rooms, as floor, ceiling or interior wall decorations.

[0022] In the process described here, the preparation of wood-containing wood chips according to step a) is carried out first, which can essentially be any wood that has been roughly crushed so that it can be prepared as wood chips.

[0023] The wood used is essentially not limited, and may be selected from, for example, pine, spruce, larch, birch, beech, dead oak, alder, etc., but is not limited thereto.

[0024] Logs may be processed into wood chips, for example by roughly chopping the wood used as raw material and by peeling it and removing coarse impurities therefrom, i.e., removing sand or stones therefrom. The size of the wood chips is essentially unlimited, as known to those skilled in the art of producing fiberboards.

[0025] According to step b), the process comprises a step of heat treating the wood chips in one or more heat treatment devices. In this step, the wood chips may be treated with steam or hot water under pressure, for example to remove VOCs from the wood beforehand. The temperature in this step may therefore be at least partially in the range above 100° C. Furthermore, the heat treatment(s) may serve to further purify the wood chips.

[0026] According to step c), the wood chips are crushed in a refiner, in which the previously coarsely crushed wood is further crushed to obtain a shape suitable for the board to be produced. This can be adjusted, for example, by adjusting the grinding mechanism or the energy introduced into the wood chips and / or the duration of the treatment of the wood chips, as is generally known to the person skilled in the art. In particular, this step can include a step of defibrating the wood chips.

[0027] The crushed or defibrated wood chips obtained after step c) are then glued according to step d). Gluing is understood to mean in particular the introduction of the wood chips into a matrix containing a binder that acts as an adhesive. The binder or adhesive can be, for example, a urea-formaldehyde resin, for example reinforced with melamine or phenol. Furthermore, it is preferred that the adhesive or binder is curable, for example by applying heat, so that after curing a stable structure is formed, which can act as the corresponding fiberboard.

[0028] The defibrated and glued wood chips may then be pressed according to step e) to form a fiberboard, in particular by applying heat and / or electromagnetic radiation. Naturally, the specific parameters applied in this step depend on the material to be pressed, in particular the adhesive or binder used.

[0029] In the process described herein, it is further provided that, according to step f), the steam used or generated in the process is separated from the process in a controlled manner at at least one steam discharge location, and the steam is separated in a predetermined amount range, the lower and upper limits of the total separated steam amount range being determined according to at least one specification of the wood chips used in step a). The separation of steam can be preferably carried out continuously. Continuous separation of steam includes, for example, uninterrupted separation or intermittent periodic separation, thus including definable periodically repeated pauses.

[0030] In particular, significant advantages can be achieved compared to related art solutions by separating the steam used or generated in the process in a controlled manner from the process at at least one steam discharge location, the steam being separated in a predetermined amount range, the lower and upper limits of the amount range of the total separated steam being determined depending on at least one specification of the wood chips used in step a).

[0031] The invention is particularly based on the fact that VOCs accumulate in the steam, and therefore by separating the steam from the process, the VOCs can be separated from the product stream, and thus, with the corresponding steam separation, the VOC emissions, such as exhaust gases or fumes, from the manufactured product, i.e., the manufactured fiberboard, are reduced.

[0032] Surprisingly, it has been found that it is not necessary to continuously separate a large amount of steam from the process to achieve a significant reduction in VOC emissions.Rather, it has been found that even a relatively small amount of steam discharge can remove almost the entire amount of VOCs, especially terpenes.This allows a significant reduction in the amount of steam removed, and therefore, for example, the amount of steam that is further processed.This reduces the overall process complexity and therefore costs.

[0033] Furthermore, in the manufacture of fiberboards, it is often necessary to generate additional steam in addition to the steam already generated during the process in order to obtain a sufficient amount of steam for the corresponding processing steps. However, the generation of steam is also associated with complexities and costs, which can be significantly reduced by the present invention.

[0034] The process described herein also takes advantage of the finding that exhaust vapor streams or even vapor streams generally having temperatures below 100° C. can contain significant amounts of volatile organic substances, particularly terpenes, even though terpenes, the most important VOCs in the process, have boiling points above 150° C. Therefore, the process described herein advantageously focuses on the total separation of vapors, regardless of their source or local separation point.

[0035] Separation of the vapor stream may be carried out essentially using relevant techniques, and advantageously the vapors are treated to recover the VOCs and are not released directly into the environment together with the VOCs. For example, the vapors may be separated using overpressure or underpressure.

[0036] The step of separating steam in a range of amounts, the lower and upper limits of which depend on at least one specification of the wood chips used in step a), can be carried out in various ways, as will be described in more detail below. According to the process described herein, the fiberboards produced may be further processed, in particular depending on their specific field of application. For example, the produced fiberboards may be ground or sawn into smaller boards, or additional layers may be applied, for example by lamination. Furthermore, certain structures may be introduced into the boards, which may serve the function of adhesion with each other or with other substrates. In this way, the fiberboards may be advantageously tailored to the desired application.

[0037] It should be mentioned that with regard to the at least one specification of the wood chips, only one specification may serve as a criterion for determining the amount of steam to be separated, or preferably multiple specifications may serve as a criterion for determining the amount of steam to be separated.

[0038] For example, the specification or specifications may be selected from the following specifications:

[0039] In particular, the specification may be the amount of wood chips used in the process. The amount of both wood chips and steam may be absolute amounts, for example in a batch process, or the amount of both wood chips and steam may be amounts per unit time, for example in a continuous process. It can be understood that, regardless of the specific composition and composition of the wood chips, the amount of wood chips has a significant impact on the VOCs introduced by the wood into the process, and thus on the VOCs emitted as well, and therefore, when determining the amount of steam to be separated, the amount of wood chips should preferably be taken into account.

[0040] Instead of or preferably in addition to the amount of wood chips used, it may be preferable that the lower and upper limits of the amount range are determined according to the amount of VOCs, especially terpene, contained in the wood chips prepared in step a).Therefore, it can be determined or estimated how much VOCs are present in wood, especially how much terpene is present in wood, especially relative to the amount of wood chips.In other words, it can be considered the amount of terpene or VOCs present in wood chips in weight percent based on the amount of wood chips.

[0041] This specification can be particularly advantageous since different types of wood have been shown to also have different amounts of terpenes, and therefore the amount of VOCs present in a particular amount of wood chips may depend on the specific type of wood used.

[0042] By selecting such a specification, the amount of steam separated can be particularly reliably reduced, since it has been determined that due to the fluctuations of VOCs occurring during the separation of the steam, not a small amount of steam is separated and therefore undesirable large amounts of VOCs are generated. Moreover, the amount of steam separated and the amount of steam that can be generated can also be reliably reduced without the aforementioned risks.

[0043] It may also be advantageous for the amount of VOCs, in particular terpenes, contained in the wood chips used in step a), to be determined by testing the wood chips used or estimated based on the type of wood chips used.

[0044] Determining the amount of VOCs by inspecting the wood chips can allow a particularly accurate determination of the VOCs contained in the wood chips, so that the determination of the amount of separated vapors can also be carried out very accurately. Here, the amount of VOCs can be determined in a known manner by analyzing the components of the wood chips. This can be advantageous, for example, since the content of VOCs can be reduced simply due to the emission of fumes during storage or due to variations in the VOCs contained in the same type of wood.

[0045] Estimating the VOCs, especially terpenes, contained in wood chips based on the type of wood chips used, especially taking into account which type of wood the wood chips are formed from, can allow a particularly simple determination of the amount of VOCs, minimizing the complexity. This arrangement can be based on the fact that different types of wood, such as birch or spruce, often have different amounts of VOCs, for example terpenes, but the amount of VOCs contained, especially the amount of terpenes contained, is characteristic of the type of wood. Thus, by knowing the type of wood used, the amount of VOCs can be estimated in advance without carrying out an analysis.

[0046] To ensure that possible inaccuracies in the VOC amount of each piece of wood are not critical, the amount of separated steam can be determined including a definable safety factor, i.e. a significantly larger amount of steam may be separated than would be required according to the utilized data on the amount of terpenes, which also makes it possible to reduce the amount of VOC removed from the process in a particularly safe and reliable manner.

[0047] It has been found that the total amount of steam separated in step f) is sufficient based on the amount of terpenes in the wood chips provided, in the range of 0.5 to 100 times its mass, preferably 0.5 to 50 times its mass, more preferably 0.5 to 10 times its mass. This amount is significantly less than the amount of steam separated from the related art, for example in the solution in US 4,925,527, but surprisingly enough to essentially remove the total amount of VOCs from the process, thus significantly reducing the VOC emissions in the process for producing fiberboards described herein. Thus, for example, when the amount of steam separated in the process or processes described herein is based on the amount of VOCs, such as terpenes, introduced into the process by the wood chips, it has been shown that a surprisingly small amount of steam can be separated, which is sufficient to solve the problem according to the present invention.

[0048] Alternatively or additionally, the dry mass of the prepared wood chips can also be a good indicator for determining the amount of steam separated. Therefore, it can be advantageous that the total amount of steam separated in step f) is within the range of 0.001-0.2 times the dry mass of the prepared wood chips, preferably 0.001-0.1 times the mass, more preferably 0.001-0.02 times the mass.

[0049] Even with such a correlation, the amount of steam separated is significantly less than that separated from the related art, for example in the solution in U.S. Pat. No. 4,925,527, but is also surprisingly sufficient to remove almost the total amount of VOCs from the process, thus significantly reducing the VOC emissions in the process for producing fiberboard described herein. Thus, for example, when the process or the amount of steam separated in the process described herein is based on the dry mass of wood chips provided, it is also shown that a surprisingly small amount of steam can be separated, which is sufficient to solve the problem according to the invention.

[0050] Here, the dry mass of wood or wood chips refers in particular to absolutely dry wood, as is customary in wood processing in general. Moreover, the dry mass of the wood used can be determined or estimated analytically on the basis of known data for the type of wood used. Moreover, in continuous or batch processes, the mass can be easily determined as an amount per unit time or as an absolute amount, as described above.

[0051] It has also been shown to be advantageous for at least one steam discharge location to be located upstream of the refiner, i.e., in the processing sequence prior to the refiner. It has been shown that a significant amount of VOCs is already removed from the wood prior to the refiner, and therefore it is advantageous to remove the VOCs from the process by steam separation prior to the refiner. On the one hand, this can achieve effective VOC removal. Moreover, it can prevent VOCs from being carried away in the process, which can make their removal more difficult.

[0052] With regard to the arrangement upstream of the refiner, it may be particularly advantageous for the steam discharge location arranged upstream of the refiner to include a heat treatment device or to be arranged between the refiner and a heat treatment device such as a cooker. It has been shown that VOCs, particularly terpenes, can be effectively removed from the process by steam separation in these arrangements, making it possible to carry out the process particularly effectively in this structure. It may therefore also be advantageous for the steam discharge location to be a steam treatment device prior to the wood chip cooker, or the wood chip cooker itself, or to be located between the steam treatment device and the cooker. It has also been shown that VOCs, particularly terpenes, can be effectively removed from the process at these discharge locations.

[0053] Here, a steam separation upstream of a location, such as upstream of a refiner, may be a location in the main material stream of wood chips or a steam recirculation that flows in the opposite direction to the main material stream, but may still be described as upstream because the location is adjacent to a corresponding location in the main material stream or because of the routing of the steam recirculation. Thus, for example, a steam recirculation from a refiner to a heat treatment device should be considered upstream of the refiner.

[0054] As mentioned above, it can be very effective to separate steam at a steam discharge location upstream of one or more refiners.In particular, since the process described herein is characterized by the fact that only a very small amount of steam is separated, it can be advantageous for at least one steam discharge location to be located downstream of the refiner, in order to allow particularly effective steam separation and to remove VOCs as completely as possible from the process.This structure can therefore exclude terpenes from the process downstream of the refiner without having to remove them all upstream of the refiner.

[0055] Particularly in this structure, the reduction in VOC emissions can be particularly effectively reduced.

[0056] From the point of view of an effective reduction of VOC emissions, it can be particularly advantageous for the steam discharge location located downstream of the refiner to be a steam separator located downstream of the refiner. A steam separator is understood to be a device intended to remove steam from the process. Thus, in addition to an effective VOC reduction, the present structure can also be implemented without the need for complex equipment.

[0057] It may also be preferred that at least one vapor discharge location is generated from the liquid stream, in which case vapor can then be generated from a corresponding hot liquid stream and then separated, or a cooler liquid stream from which no vapor is generated can be heated until vapor is generated in order to separate the vapor stream thus generated.

[0058] This design allows for the fact that VOCs or terpenes escaping from the wood not only accumulate in the vapor, but are also found in at least small amounts in the liquid streams. By venting the vapor from these liquid streams, this portion of the VOCs can then be effectively removed from the process, thereby further enhancing the overall effectiveness of the reduction of VOCs.

[0059] Examples of liquid streams in which VOCs may be found include the squeeze water stream coming directly from the compaction screw, or the liquid stream resulting from the squeeze water stream coming from the compaction screw.

[0060] It may also be advantageous to collect the VOC-containing vapors removed according to step g) and, optionally, further process one or more components. Due to the possibility of collecting the separated vapor stream in this structure and possibly further processing them, the process not only serves to reduce VOC emissions in this way, but can also be carried out much more economically. This is because the materials contained in the vapor stream, or other properties of the vapor stream, such as its heat, can be used in this or other processes, thereby saving costs and resources.

[0061] For example, it may be advantageous to isolate a mixture of terpenes or turpentine as a further treatment. While such substances should be actually reduced as an emission of the process for producing fiberboard to prevent their release into the environment, they may be valuable products for other processes or uses. Thus, this structure may be particularly advantageous from the point of view of the economy of the process described here and from the point of view of value creation of the wood used. The same is true when, as a further treatment, hydrates are isolated. Within the meaning of the present invention, hydrates are generally understood to be the aqueous phase obtained after condensation of the steam, which may contain the respective water-soluble components, such as formaldehyde.

[0062] Additionally, it may be advantageous for the separated vapor or one or more components to be further processed by combustion, or exposure to high temperatures, adsorption, absorption, membrane technology techniques, condensation, crystallization, or other suitable process engineering techniques.

[0063] Combustion or exposure to high temperatures allows, for example, thermal re-burning of the VOCs contained in the separated vapor stream, and thereby potentially the use of energy. Each of the other mentioned techniques may refer to the isolation or separation of individual substances.

[0064] It may also be advantageous that the heat of the material streams generated in the process, for example the separated steam stream, is reused as energy in the process. In this configuration, the energy contained in the material streams in the form of heat can thus be reused, in particular for heating other material streams. This step may also improve the economic aspects of the process according to the invention, thus saving costs and resources.

[0065] The invention will now be described in more detail and by way of example with reference to the accompanying drawings using preferred exemplary embodiments, the features set out below which can both individually and in combination represent aspects of the invention. [Brief description of the drawings]

[0066] [Figure 1] FIG. 1 is a schematic representation of the process according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] In Figure 1 the process according to the invention is shown diagrammatically, where the solid arrows are intended to represent the main material flows and the dashed arrows are intended to indicate the recirculation of steam.

[0068] In step 10, wood chips are provided. These are essentially formed from selectable wood and are provided by rough crushing, in particular by rough cleaning, of the wood.

[0069] The wood chips are then treated in a number of heat treatment devices. This is accomplished in a first heat treatment step 20, a second heat treatment step 40, and a third heat treatment step 50.

[0070] Within the meaning of the present invention, it is generally defined that the VOC-containing exhaust gas has a high temperature, which means in particular a temperature higher than the boiling point of water, i.e. 100° C., which temperature may also be present at least partially during the heat treatment.

[0071] The first heat treatment step 20 is carried out in a so-called pre-pre-vapor container at a preferred temperature of up to about 100° C., in particular under atmospheric pressure. This is the first heat treatment of the wood chips, which is carried out using steam, preferably water vapor. Here, a part of the VOCs can be transferred from the wood chips to the steam. This VOC-containing steam can be removed from the first heat treatment device at the steam discharge point, preferably from the top of the device and via a pipeline located, for example, on the roof.

[0072] Subsequently, the wood chips are washed or cleaned in a cleaning step 30 before the second heat treatment step 40. Cleaning of the wood chips in the cleaning device is carried out in particular at a temperature above room temperature and below the boiling point of water, in particular between 80°C and 100°C. The high temperature allows a better separation of the wood chips and the foreign matter. In this way, the foreign matter that is not wood chips is filtered and removed from the processing system. Cleaning of the wood chips is preferably carried out with a water-containing, in particular water-based, medium.

[0073] It is an advantageous option for the cleaning device to receive the VOC-containing condensate from the first heat treatment device described above, which can be removed from the processing system together with the VOCs released during cleaning.

[0074] The second heat treatment step 40 of the wood chips is carried out in a second heat treatment device, also called a pre-vapor container, which is configured to receive and dissipate VOC-containing exhaust gases, in particular back to the first heat treatment device. The second heat treatment is carried out, for example, without pressure and at a temperature above room temperature, in particular below the boiling point of water, i.e. below 100°C. The high temperature allows for better release of VOCs from the wood chips. The VOC-containing exhaust gases are in particular dissipated from the second heat treatment device and / or sent to the first heat treatment device. Furthermore, VOC-containing exhaust gases from devices used later to carry out the process can be fed to the second heat treatment device to further heat the wood chips or to release VOCs.

[0075] As an example, and independent of other features, the second heat treatment of the wood chips in the second heat treatment device may be carried out using steam, preferably water steam. Here, a part of the VOCs may be transferred from the wood chips to the steam. This VOC-containing steam may be dissipated from the second heat treatment device, preferably from its top, for example through a pipeline located on the roof. Instead of or in addition to dissipating the VOC-containing steam, some or all of the steam may be condensed and release the VOCs from the wood chips as condensate. This VOC-containing condensate may be sent to, for example, a compaction screw, a cooker, and / or a water treatment plant.

[0076] The third heat treatment step 50 may in particular be carried out in a so-called cooker. The cooking of the wood chips in the cooker, which may be arranged to receive and dissipate the VOC-containing exhaust gas, is carried out, for example, at a temperature above room temperature, in particular between 3 bar and 15 bar (inclusive), preferably between 5 bar and 13 bar (inclusive), preferably at 9 bar, at a temperature above the boiling point of water, i.e. 100°C, for example between 90 and 175°C. The high temperature allows a better release of the VOCs from the wood chips. The cleaning of the wood chips is preferably carried out in a water-containing, in particular water-based, medium. The first and second heat treatments heat and soften the wood chips, so that the VOCs contained in them are efficiently released from the cooker. A droplet separator is preferably connected downstream of the cooker.

[0077] Receiving said VOC-containing condensate from the second heat treatment device is an advantageous option for the consolidation screw upstream of the cooker and / or the cooker itself, which can be dissipated from the processing system via the consolidation screw and / or via the cooker together with the VOCs optionally released during cooking.

[0078] The wood chips are subsequently crushed in a refiner in a crushing or defibrating step 60. The refiner's structure and operation can be adaptable to the desired application of the board. In principle, a crushing energy of 50 to 200 kWh per ton of wood chips can be introduced via a crushing tool that is part of the refiner and defibrates the wood chips. Lower crushing energies, such as about 50 kWh per ton of wood chips, are suitable for flooring, and 150 kWh per ton of wood chips is suitable for high quality furniture.

[0079] Starting from the refiner, the thus obtained defibrated wood chips or wood fibres are guided through a so-called blowline, where a drying step 70 for drying the wood fibres coming from the refiner is carried out in a dryer, which may be carried out again at high temperature, where the resulting humid atmosphere may be removed from the wood fibres by a separation step 80. The exhaust air may for example be washed so that the remaining components, in particular VOC-containing components, can be washed off and can be reused or recovered.

[0080] The dried defibrated wood chips or wood fibers thus obtained are processed into fiberboards in a processing step 90. For this purpose, the defibrated wood chips may be glued and the glued defibrated wood chips may be pressed into boards, which may then be subjected to final processing for a particular application.

[0081] In the process described herein, steam is generated or additional steam is provided. In order to advantageously remove VOCs generated from the raw wood during the process, it is provided that the steam used or generated in the process is continuously separated from the process at at least one steam discharge location, and the steam is separated in a predetermined amount range, the lower and upper limits of the total amount range of separated steam being determined according to at least one specification of the wood chips used in step a).

[0082] Thus, the separation of steam to remove VOCs depends on the VOCs introduced into the process by the wood chips or their wood. This can be carried out, for example, taking into account the amount and / or type of wood introduced or specifically the amount of VOCs introduced. In particular, the total amount of steam separation can be in the amount range of 0.5 to 100 times the mass of the terpene amount of the wood chips provided, preferably 0.5 to 50 times the mass, more preferably 0.5 to 10 times the mass. Alternatively or additionally, the total amount of steam separation can be in the amount range of 0.001 to 0.2 times the mass of the wood chips provided, preferably 0.001 to 0.1 times the mass, more preferably 0.001 to 0.02 times the mass, based on the dry mass of the wood chips provided.

[0083] Various vapor discharge locations can be used to separate the vapors and thus remove the VOCs. A vapor discharge location is understood to be in particular a location where the vapors can be separated from the process.

[0084] For example, the following steam discharge locations are suitable for separating steam: pre-pre steam vessel or first heat treatment device, pre-steam vessel or second heat treatment device, cooker or third heat treatment device, or refiner. After the first heat treatment device, a conveying unit such as a screw or conveying device between the second and third heat treatment device, or a conveying unit such as a screw between the third heat treatment device and the refiner are also suitable. A dewatering unit such as a dewatering screw, or recirculation of steam between individual process units are also suitable.

[0085] However, the following gas exhaust locations have been found to be particularly suitable.

[0086] For example, at least one gas discharge location can be located upstream of the refiner, including, for example, a location in the heat treatment device or in the steam recirculation between the refiner and the heat treatment device, in a steam treatment device prior to the wood chip cooker or in the wood chip cooker itself, or in the steam recirculation between the steam treatment device and the cooker.

[0087] Alternatively or additionally, it may be advantageous for at least one steam discharge location to be located downstream of the refiner. In this connection, it is advantageous for the steam discharge location located downstream of the refiner to be a steam separator located downstream of the refiner.

[0088] Furthermore, it may be particularly preferred that at least one steam discharge location is generated from a liquid stream, for example a squeezed water stream coming directly from the compaction screw or a liquid stream resulting from the squeezed water stream coming from the compaction screw.

[0089] The processes described herein allow for a cost and resource saving method for reducing VOC emissions in the manufacture of fiberboard, particularly HDF or MDF board. [Explanation of symbols]

[0090] 10. Wood chip preparation process 20 First heat treatment process 30 Cleaning process 40 Second heat treatment process 50 Third heat treatment process 60 Crushing process 70 Drying process 80 Separation process 90 Processing process

Claims

1. 1. A process for producing fiberboard having reduced VOC emissions, comprising: a) providing wood chips containing wood; b) heat treating the wood chips in a heat treatment device or in a plurality of heat treatment devices; c) crushing the wood chips in a refiner; d) gluing the wood chips; e) compressing the bonded wood chips to form the fiberboard; At least f) steam used or produced in the process is continuously separated from the process in a controlled manner at at least one steam discharge location; The total amount of separated steam is The dry mass of the wood chips used in step a) is in the range of 0.001 to 0.2 times; or The amount of VOCs, particularly terpenes, contained in the wood chips used in step a) is in the range of 0.5 to 100 times.

2. 2. The process according to claim 1, characterized in that the amount of VOCs, in particular terpenes, contained in the wood chips used in step a) is determined by testing the wood chips used or is estimated based on the type of wood chips used.

3. 10. The process of claim 1, wherein at least one steam discharge location is located upstream of the refiner.

4. 4. The process of claim 3, wherein the steam discharge location located upstream of the refiner includes a heat treatment device or is located between the refiner and a heat treatment device.

5. 4. The process of claim 3, wherein the steam discharge location located upstream of the refiner is a steam treatment device prior to a wood chip cooker, or the wood chip cooker itself, or is located between the steam treatment device and the wood chip cooker.

6. 10. The process of claim 1, wherein at least one steam discharge location is located downstream of the refiner.

7. 7. The process of claim 6, wherein the steam discharge location downstream of the refiner is a steam separator downstream of the refiner.

8. 10. The process of claim 1, wherein at least one vapor discharge location is generated from the liquid stream.

9. 9. The process according to claim 8, characterized in that the liquid stream is a pressed water stream coming directly from a compaction screw or a liquid stream resulting from a pressed water stream coming from a compaction screw.

10. 2. The process of claim 1, wherein the VOC-containing vapors removed according to step f) are collected and, optionally, one or more components are further processed.

11. 11. The process according to claim 10, characterized in that as a further processing, the mixture of terpenes or turpentine is isolated.

12. 11. The process according to claim 10, characterized in that as a further processing, the hydrate is isolated.

13. 11. The process of claim 10, wherein the separated vapor or one or more components are further treated by combustion, or exposure to high temperatures, adsorption, absorption, membrane technology techniques, condensation, crystallization, or other suitable process engineering techniques.

14. 2. The process of claim 1, wherein heat of the material streams generated in the process is reused as energy in the process.

15. 2. The process of claim 1, wherein heat of the separated vapor stream is reused as energy in the process.

16. 2. Process according to claim 1, characterized in that it is a thermomechanical process by which MDF or HDF boards are produced.

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