Method for manufacturing fiberboard with reduced VOC emissions

Abstract

The invention relates to a method for manufacturing fiber boards with reduced VOC emissions.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing fiber boards with reduced VOC emissions, in particular a method for manufacturing HDF boards or MDF boards. BACKGROUND

[0002] Continuous processes for manufacturing wood fibers based on lignocellulosic materials such as wood, straw or bagasse using dry and wet technologies include but are not limited to chopping the raw material into free fibers or fiber aggregates, coating the free fibers or fiber aggregates with glue in a subsequent step, drying, forming and pressing into the final product, so-called boards or fiber boards. Today, the liberation of fibers from the raw material is preferably carried out in a single step in a so-called thermo mechanical process or in at least two separate steps in a thermo and mechanical process.

[0003] Prior to the first heat treatment, the wood chips are usually washed to remove any contaminants, such as dirt or stones. The heat treatment, i.e. the heating of the raw material, is carried out, for example, in a first heat treatment device at a preferred temperature of up to about 100°C, in particular at atmospheric pressure, and subsequently in a second heat treatment device, which is preferably pressurized, at a temperature of, for example, about 150°C to 190°C, in particular at a pressure of about 4 bar to 13 bar. The residence time of the wood chips in the heat treatment device can be adjusted depending on the prevailing process conditions and can be, for example, between about 1 minute to 10 minutes. According to the relevant technology, the heating in the second heat treatment device is preferably carried out with the aid of steam. Mechanical processing is then carried out in a refiner, also called a fiber separator. The residence time of the wood chip raw material in the refiner is short. The energy converted into mechanical energy associated with the mechanical processing is converted into heat in the size reduction zone and appears in the processing system as exhaust gas, in particular steam, which is produced from the moisture in the raw material.

[0004] After the fiber separation in the refiner, the wood fibers are usually pneumatically conveyed to a fiber dryer, in which a drying process is carried out depending on the current fiber moisture at a large amount of air and a controlled inlet air temperature of about 140°C to 200°C. The fibers are mechanically separated from the drying air. The dried fibers are then conveyed for the forming, pre-pressing and final pressing of the board. The drying air is subjected to an exhaust gas scrubbing. For this purpose, wet scrubbing, wet electrofilters or biological filters, and biological waste water treatment are used.

[0005] According to the related art, wood emissions released during the release and drying of the fibrous material, in particular in the second heat treatment device, are conveyed from the first heat treatment device via the refiner to the dryer, in which the majority is separated from the fibers, and finally the moist drying air from the dryer is guided to the atmosphere after exhaust gas scrubbing. These wood emissions mainly contain volatile organic substances, so-called volatile organic compounds (VOC).

[0006] Among the VOCs, there are substances whose water solubility in the moist exhaust gas scrubbing is very small, so that their degree of separation is only a few percent or even close to zero. This applies in particular to terpenes. Thus, the known wet separation process achieves only a degree of emission reduction of 10% to 30%. The low solubility is due to the low solubility of the substances in water and the strong dilution in the drying air, which greatly reduces the partial pressure and thus the thermodynamic driving force. Terpenes originate from the resin of the wood used. They are volatile oils. They are also known as turpentine.

[0007] The remaining amount that does not leave the dryer enters the subsequent processing units with the fiber flow, in which they are successively released into the surrounding atmosphere or occur as residual products in the final product (board). Thus, emissions can also be emitted from the final product into the atmosphere.

[0008] It is already known from WO 99 / 10594 that the second heat treatment device is provided with an upper outlet for degassing the organic emissions released at the upper outlet. Here, steam is introduced into the lower part of the first heat treatment device and the wood chips that intrude into the upper part of the first heat treatment device are washed in the steam condensation in the countercurrent 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 released emissions, exhaust air and steam resulting from the evaporation of moisture from the wood chips are separated and disposed of by the outlet of the respective device. This publication also discloses that the wood chips from the first heat treatment device are conveyed to the refiner by means of a screw conveyor, which compresses and exhausts the wood chips during the conveying process.

[0009] According to the publication EP 1597427 A1, a method is known in which the exhaust gas produced during compression is disposed of in the screw conveyor via an outlet arranged in the compression zone. The device according to this document is characterized in that an exhaust gas outlet for emitting the evaporated moisture is arranged in the compression zone, which evaporated moisture is produced when the wood chips are compressed and contains VOC-containing exhaust gas.

[0010] EP 2 573 258 A1 describes a method and an apparatus for processing wood chips to produce a fiber material containing wood. With regard to the washing of the wood chips, it is stated that this is done by heating to about 90°C using water heated to 98°C.

[0011] US 4,925,527 describes a method for recovering turpentine in a TMP (thermomechanical pulp) process, wherein a gas stream is taken from the refiner and fed to a condenser.

[0012] EP 1 021 612 A1 describes an apparatus for producing and processing wood fibers, the apparatus comprising a fiber production section provided with a wood chip preheater and a beater for liberating fibers from wood chips, and at least one dryer section for drying the fibers. Between the fiber production section and the dryer section a vapor separator section is provided, comprising a cyclone separator, the inlet of which is connected to a blower line for fibers and vapor obtained from the beater machine. A lower outlet of the cyclone separator is connected via a gate to a conveying / drying line for fibers. An upper outlet of the cyclone separator is connected to means for separating volatile organic substances and recovering heat from the vapor of the cyclone separator.

[0013] US2012 / 227918 A1 describes a refiner vapor separation system comprising a blow line for conveying a mixture of fiber material from a refiner to an inlet of a vapor separator. Exhaust vapor is discharged from the separator via an exhaust vapor outlet. Clean fiber material is discharged from the separator via an outlet, which prevents a significant portion of the exhaust vapor from reaching the outlet. A relay pipe is connected to the outlet and a dryer conduit and conveys clean fiber material between the two. A resin inlet is connected to the relay pipe and supplies resin thereto. The resin is mixed with the clean fiber material before drying the clean fiber material in the dryer conduit.

[0014] However, for an environmentally friendly wood processing, it is necessary to remove VOCs even more efficiently from the process of producing fiber boards, in particular of producing HDF boards or MDF boards, wherein a resource-saving process should also be achieved. SUMMARY

[0015] According to the invention, a solution to the problem is achieved by the method for manufacturing fiber boards with reduced VOC emissions having the features of claim 1. Preferred configurations of the invention are given in the dependent claims and the following description, each of which can represent aspects of the invention individually or in combination.

[0016] A method for manufacturing a fiberboard with reduced VOC emissions is described, wherein the method comprises at least the following method steps:

[0017] a) providing wood-containing wood chips;

[0018] b) heat-treating the wood chips in one heat-treatment device or in a plurality of heat-treatment devices;

[0019] c) chopping, in particular fiber-separating, the wood chips in a refiner;

[0020] d) gluing the chopped, in particular fiber-separated, wood chips; and

[0021] e) pressing the chopped, in particular fiber-separated and glued, wood chips to form the fiberboard,

[0022] wherein

[0023] f) separating, in particular continuously separating, the vapors used or produced in the method in a controlled manner from the method at at least one vapor separation location, wherein the vapors are separated in a predetermined content range, such that the lower and upper limits of the content range of the total separated vapors depend on at least one specification of the wood chips used in method step a).

[0024] This method allows a particularly advantageous way to efficiently reduce VOC emissions, which are harmful to the environment, in the production of fiberboards. Furthermore, a resource-saving method is possible.

[0025] 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 a raw material for the method described herein. In particular, the volatile organic compounds referred to in this method are terpenes, which are present in the form of wood oil in the wood. Examples include the following substances, which can be present in the weight percentages based on the contained VOC given in parentheses: a-pinene (20% to 70%), β-pinene (5% to 20%), limonene (1% to 5%), camphene (1% to 5%), phenol (0.2% to 2%). Other components can include myrcene, α-phellandrene, β-phellandrene, 3-carene, cymene, terpineol, roclene.

[0026] The term "controlled" within the meaning of the present invention means that the content of the vapors to be separated and / or the material flow is adjustable, preferably controllable, in terms of vapor separation. In this respect, vapor separation locations that are not adjustable and / or not controllable are not to be understood as controlled vapor separation within the meaning of the present invention.

[0027] The method described herein is used for the production of fiber boards. A fiber board within the meaning of the invention is understood in the generally known manner as a board having wood fibers in a matrix comprising a binder. For example, the fiber board can be a so-called medium density fiber board (MDF board, density of for example 700 to 800 kg / m 3 ) or a low density fiber board (LDF, density of for example less than 650 kg / m 3 ). Furthermore, so-called high density fiber boards (HDF board, density of for example more than 800 kg / m 3 ) can be produced using the described method. More preferably, MDF boards or HDF boards can be produced using the described method. Such fiber boards are particularly suitable for use as underlay for indoor finishing of roofs or as an outer cladding of walls. The boards are also widely used for the production of furniture. It is also suitable to apply them as floor, ceiling or wall coverings for the interior fitting of a room.

[0028] In the method described herein, wood-containing wood chips according to method step a) are first provided. In this step, essentially any wood can be provided, which is roughly cut up so that it can be provided as wood chips.

[0029] The wood used is essentially not limited, for example, wood selected from the group consisting of pine, spruce, larch, birch, beech, dead oak, alder and the like can be used, but is not limited thereto.

[0030] The raw wood can be processed into wood chips, for example, by roughly cutting the wood used as raw material and debarking it and removing coarse impurities therefrom, i.e., for example, making it free of sand components or stones. The size of the wood chips is essentially not limited as known to the person skilled in the art in the field of fiber board production.

[0031] According to method step b), the method comprises heat treating the wood chips in one heat treatment device or in a plurality of heat treatment devices. In this method step, the wood chips can be treated with steam or pressurized hot water, for example, thereby removing VOCs from the wood. The temperature in this method step can thus be at least partially in the range above 100°C. In addition, the one or more heat treatments can serve to further clean the wood chips.

[0032] According to method step c), the wood chips are cut up in a refiner. In this method step, the wood, which has previously been roughly cut up, is further cut up so that it assumes a form 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 wood chip treatment, as generally known to any person skilled in the art. In particular, this method step can comprise fiber separation of the wood chips.

[0033] The wood chips obtained after method step c) are then glued according to method step d). Gluing is understood to mean in particular the introduction of the wood chips into a matrix comprising a binder used as glue. The binder or glue can be, for example, a urea-formaldehyde resin, for example reinforced with melamine or phenol. In addition, the glue or binder is preferably curable, for example by the application of heat, so that after curing a stable structure is formed which can be used as a corresponding fiberboard.

[0034] The fiber-separated and glued wood chips can thus be pressed according to method step e) to form a fiberboard, in particular by the application of heat and / or electromagnetic radiation. It can be understood that the specific parameters applied in this method step depend on the material to be pressed, in particular the glue or binder used.

[0035] In the method described here, it is further provided that, according to method step f), vapors used or produced in the method are separated from the method in a controlled manner at at least one vapor discharge location, wherein the vapors are separated in a predetermined content range, so that the lower and upper limits of the content range of the total separated vapors depend on at least one specification of the wood chips used in method step a). The separation of the vapors can preferably be carried out continuously. For example, continuous separation of the vapors includes uninterrupted separation or continuous periodic separation, thus including a definable periodic recurring pause.

[0036] In particular, by separating vapors used or produced in the method from the method in a controlled manner at at least one vapor discharge location, wherein the vapors are separated in a predetermined content range, so that the lower and upper limits of the content range of the total separated vapors depend on at least one specification of the wood chips used in method step a), significant advantages can be achieved compared to the solutions of the related art.

[0037] The present application is based in particular on the fact that by separating vapors from the method, VOCs can be separated from the production flow, as they accumulate in the vapors. The corresponding vapor separation thus leads to a reduction of VOC emissions, such as exhaust gases or fumes from the manufactured product, i.e. the produced fiberboard.

[0038] Surprisingly, it has been found that in order to achieve a significant reduction of VOC emissions, it is not necessary to continuously separate large amounts of vapors from the method. Rather, it has been found that even by discharging a relatively small amount of vapors, almost the entire content of VOCs, in particular terpenes, can be removed. This can significantly reduce the content of the removed vapors and thus, for example, the content of the vapors to be further processed. This can reduce the complexity of the entire method and thus the costs.

[0039] In addition, in the production of fiber boards, in addition to the steam already produced during the course of the method, it is generally necessary to produce further steam in order to obtain a sufficient amount of steam for the respective processing steps. However, the production of steam is also associated with complexity and costs which can be significantly reduced in accordance with the present application.

[0040] It has also been discovered in the method described herein that even though terpenes, which are the most important VOCs in this method, have a boiling point of more than 150°C, it has been found that even exhaust steam flows or generally steam flows at temperatures below 100°C can contain considerable amounts of volatile organic substances, in particular terpenes. Therefore, in the method described herein, it is advantageous to focus on the total separated steam content regardless of its origin or point of separation.

[0041] The separation of the steam flow can basically be carried out using the techniques of the relevant art and it is advantageous to treat the steam in order to collect the VOCs and not to release them directly to the environment together with the VOCs. For example, the steam can be separated by means of an overpressure or an underpressure.

[0042] The separation of the steam within the predetermined content range, such that the lower and upper limits of the total separated steam content range depend on at least one specification of the wood chips used in the method step a), can be achieved in various ways, as described in more detail below.

[0043] After the method described herein, the produced fiber boards can be further processed, in particular according to their specific field of application. For example, the produced fiber boards can be sanded or sawn into smaller boards or, for example, in a lamination process, further layers can be applied. Furthermore, it is possible to introduce certain structures into the boards which can serve as an attachment to one another or to other substrates. In this way, the fiber boards can advantageously be directed to the desired application.

[0044] With regard to the at least one specification of the wood chips, it should be mentioned that only one specification can be used as a basis for determining the content of the steam to be separated or, preferably, a plurality of specifications can be used as a basis for determining the content of the steam to be separated.

[0045] For example, one specification or a plurality of specifications can be selected from the following specifications.

[0046] In particular, the specification can be the content of the wood chips used in the method. For example in a batch process, the content of both the wood chips and the steam can be an absolute content or, for example in a continuous process, the content of both the wood chips and the steam can be a content per unit of time. It can be understood that the content of the wood chips significantly influences the VOCs introduced by the wood into the method and thus also the VOCs to be emitted, such that the content of the wood chips should preferably be taken into account when determining the content of the steam to be separated, regardless of the specific configuration and composition of the wood chips.

[0047] Alternatively or preferably, in addition to the content of wood chips used, it can also be preferred that the lower and upper limits of the content range depend on the content of VOC, in particular terpenes, contained in the wood chips provided in method step a). Thus, it can be determined or estimated in particular how much content of VOC is contained in the wood chips and thus how much content of terpenes is present per unit content of wood chips. In other words, based on the content of wood chips, the content of the weight percentage of terpenes or VOC present in the wood chips can be taken into account.

[0048] Such a specification can be particularly advantageous, since it has been shown that different types of wood also have different contents of terpenes. Thus, the content of VOC present in a certain content of wood chips can depend on the specific type of wood used.

[0049] In particular, by selecting such a specification, the content of the vapors to be separated can be reduced particularly reliably, since it is ensured that too little vapor is not separated and thus an undesirably large content of VOC occurs due to changes in the VOC occurring during vapor separation. In addition, the content of the vapors to be separated and possibly produced can still be reliably reduced without the above-mentioned risks.

[0050] It can also be advantageous to determine the content of VOC, in particular the content of terpenes, contained in the wood chips used in method step a) by examining the wood chips used or estimating it based on the type of wood chips used.

[0051] Determining the content of VOC by examining the wood chips can enable the VOC contained in the wood chips to be determined particularly precisely, so that the content of the vapors to be separated can also be determined very accurately. Here, the VOC content can be determined in a known manner by analyzing the components of the wood chips. This can be advantageous, for example, because the content of VOC can be reduced simply by emissions of smoke during storage or due to changes in the VOC contained in the same type of wood.

[0052] Based on the type of wood chips used, in particular taking into account which type of wood the wood chips are formed from, the estimation of the VOC, in particular terpenes, contained in the wood chips can allow the content of VOC to be determined particularly simply, wherein the complexity can be kept to a minimum. Such an arrangement can be based in particular on the fact that different types of wood, such as birch or spruce, generally have different contents of VOC, such as terpenes, but the content of the VOC contained, in particular the content of the terpenes contained, is characteristic of the type of wood. Thus, if the type of wood used is known, the content of VOC can be estimated in advance without having to carry out an analysis.

[0053] To ensure that possible inaccuracies of the VOC content of the respective wood are not critical, the separated vapor content can be determined, including a definable safety factor, i.e. based on the data on the terpene content utilized, a vapor content can be separated which is definably greater than the required content. This also allows a particularly safe and reliable reduction of the VOC content removed from the method.

[0054] It has been found that, in method step f), based on the terpene content of the wood chips provided, it is sufficient to separate a total content of the vapor in the range of 0.5 to 100 times the mass, preferably 0.5 to 50 times the mass, more preferably 0.5 to 10 times the mass. This content is significantly lower than the separated vapor content in the prior art solutions (e.g. in US 4,925,527), but surprisingly sufficient to substantially remove the entire content of VOC from the method and thus significantly reduce the VOC emissions in the method for manufacturing fiber boards described herein. It has thus been shown, for example, that when the method described herein or the content of the vapor separated in the method is based on the content of VOC such as terpenes introduced into the method by the wood chips, surprisingly little content of vapor can be separated, which is sufficient to solve the task according to the application.

[0055] Alternatively or additionally, the dry mass of the wood chips provided can also be a good indicator of the content of the vapor to be separated. It can thus be advantageous if, in method step f), based on the dry mass of the wood chips provided, the total content of the vapor separated is in the range of 0.001 to 0.2 times the mass, preferably 0.001 to 0.1 times the mass, more preferably 0.001 to 0.02 times the mass.

[0056] Even in this correlation, the content of the vapor to be separated is significantly lower than the separated vapor content in the prior art solutions (e.g. in US 4,925,527), but also surprisingly sufficient to remove almost the entire content of VOC from the method and thus significantly reduce the VOC emissions in the method for manufacturing fiber boards described herein. It has thus also been shown, for example, that when the method described herein or the content of the vapor separated in the method is based on the dry mass of the wood chips provided, surprisingly little content of vapor can be separated, which is sufficient to solve the task according to the application.

[0057] Here, the dry mass of the wood or wood chips in particular refers to atro-absolut trocken wood, which is customary in general wood processing. The dry mass of the wood used can in turn be determined analytically or estimated based on known data of the wood type used. Furthermore, the mass can easily be determined as mass per unit of time or absolute mass in a continuous or batch process, as described above.

[0058] It has also been shown to be advantageous to position at least one vapour discharge location upstream of the refiner, i.e. before the refiner in the process sequence. It has been shown that a significant content of VOCs has already been removed from the wood before the refiner, and thus that it is advantageous to remove VOCs from the process by vapour separation before the refiner. This can achieve, on the one hand, an effective VOC removal. Furthermore, it can prevent the carrying of VOCs in the process, which can make it more difficult to remove.

[0059] It can be particularly advantageous with regard to the positioning upstream of the refiner that the vapour discharge location positioned upstream of the refiner comprises a heat treatment device, or is positioned between the refiner and a heat treatment device, such as a digester. It has been shown that VOCs, in particular terpenes, can be effectively removed from the process by vapour separation at these locations, so that the process can be carried out particularly effectively in this configuration. It can thus also be advantageous for the vapour discharge location to be a vapour treatment device before the wood chip digester or the wood chip digester itself, or to be located between the vapour treatment device and the digester. It has also been shown at these discharge locations that VOCs, in particular terpenes, can be effectively removed from the process.

[0060] Here, vapour separation upstream of a location such as the refiner can be at a location of the main material flow of the wood chips or of the vapour recirculation, which, despite running in the opposite direction to the main material flow, can still be described as upstream due to its location adjacent to the corresponding location of the main material flow or due to the route of the vapour recirculation. Thus, for example, vapour recirculation from the refiner to a heat treatment device is considered to be upstream of the refiner.

[0061] As mentioned above, the separation of vapour at one or more vapour discharge locations upstream of the refiner can be very effective. In particular, since the process described here is characterised by the separation of only very small amounts of vapour, it can be advantageous in order to be able to separate the vapour particularly effectively and to remove VOCs from the process as completely as possible to position at least one vapour discharge location downstream of the refiner. This configuration thus allows the expulsion of terpenes from the process downstream of the refiner, even if not all terpenes are removed upstream of the refiner.

[0062] The reduction of VOC emissions can in particular be effectively reduced, especially in this configuration.

[0063] It can be particularly advantageous in terms of effective reduction of VOC emissions for the vapour discharge location positioned downstream of the refiner to be a vapour separator positioned downstream of the refiner. A vapour separator is understood to be a device which is intended to remove vapour from the process. This configuration can thus also be implemented without complex equipment in addition to effectively reducing VOCs.

[0064] It can also be preferred that at least one of the steam discharge locations is generated from the liquid flow. In this configuration, steam can thus occur from the respective hot liquid flow, which is then separated, or the cooler liquid flow, from which no steam occurs, can be heated until steam occurs, in order to separate the steam flow thus generated.

[0065] In this configuration, it can be considered that VOCs or terpenes escaping from the wood not only accumulate in the steam, but also exist in the liquid flow, at least in small amounts. By discharging steam from these liquid flows, these VOC fractions can then be effectively removed from the method, which can further effectively reduce VOCs overall.

[0066] Examples of liquid flows in which VOCs can be found include the extrusion water directly from the compaction screw or the liquid flow occurring from the extrusion water from the compaction screw.

[0067] It can also be advantageous to collect the VOC-containing steam removed according to method step g) and, if applicable, to further process one or more components. In this configuration, the method can thus not only be used to reduce VOC emissions, but also be carried out much more economically, due to the possibility of collecting the separated steam flows and possibly further processing them. This is due to the materials contained in the steam flows or other properties of the steam flows, such as their heat, which can be used in the method or other methods, so that costs and resources can be saved.

[0068] For example, it can be advantageous to separate a mixture of terpenes or turpentine as further processing. While such substances should indeed be reduced as emissions from the method for manufacturing fiber boards in order to prevent their release into the environment, these substances can be valuable products for other methods or applications. This configuration can thus be particularly advantageous in terms of the economy of the method described here and in terms of value creation from the wood used. The same applies if, as further processing, a hydrolate is separated. In the sense of the present invention, a hydrolate is generally understood to be the aqueous phase obtained after condensation of the steam, which can contain corresponding water-soluble components, such as formaldehyde.

[0069] Furthermore, it can be advantageous to further process the separated steam or one or more components by combustion or exposure to high temperatures, adsorption, absorption, membrane technology, condensation, crystallization or other suitable process engineering techniques.

[0070] Combustion or exposure to high temperatures allows, for example, thermal afterburning and thus possibly an energy-technical utilization of the VOCs contained in the separated steam flow. The other mentioned techniques can each refer to the separation or separation of individual substances.

[0071] It can also be advantageous to re-use the heat of the material stream (e.g. the separated vapor stream) generated in the method in an energetic manner in the method. In this configuration, the energy inherent in the material stream in the form of heat can thus be re-used, in particular for heating other material streams. This step can also improve the economic aspects of the method according to the application and thus save costs and resources.

[0072] The application will be explained in more detail below by way of example using preferred exemplary embodiments, with the features shown below being able to represent aspects of the application both individually and in combination. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 A schematic illustration of the method according to the application is shown. DETAILED DESCRIPTION

[0074] In Figure 1 In the figure, a method according to the application is shown schematically. Here, the solid arrows are intended to indicate the main material stream and the dashed arrows are intended to show the vapor recirculation.

[0075] In step 10, wood chips are provided. These are formed from substantially selectable wood and are provided by a rough reduction in the size of the wood and in particular by a rough washing.

[0076] Subsequently, the wood chips are treated in a plurality of thermal treatment devices. This is achieved in a first thermal treatment step 20, a second thermal treatment step 40 and a third thermal treatment step 50.

[0077] Within the meaning of the application, a VOC-containing exhaust gas having a high temperature is generally provided. This particularly means a temperature greater than the boiling point of water, i.e. 100°C, so that this temperature is present at least partially during the thermal treatment.

[0078] The first thermal 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 at atmospheric pressure. This is the first thermal treatment of the wood chips and is carried out using a vapor, preferably water vapor. Here, a portion of the VOCs can be transferred from the wood chips into the vapor. This VOC-containing vapor can be removed from the first thermal treatment device at a vapor discharge location, preferably from the upper portion of the device, and for example via a line arranged on the top.

[0079] Subsequently, the wood chips are washed or cleaned in a cleaning step 30 prior to the second heat treatment step 40. The cleaning of the wood chips in the washing device is in particular carried out at a temperature above room temperature and below or equal to the boiling point of water, in particular between 80°C and 100°C. The elevated temperature allows a better separation of the wood chips from foreign substances. Thus, foreign substances that are not wood chips are filtered out and removed from the processing system. The cleaning of the wood chips is preferably carried out with an aqueous medium, in particular a water-based medium.

[0080] It is an advantageous option that the washing device receives the aforementioned condensate containing VOCs from the first heat treatment device. This condensate containing VOCs can be removed from the processing system together with the VOCs released in the washing process.

[0081] The second heat treatment step 40 of the wood chips is carried out in a second heat treatment device, also referred to as pre-vapor vessel, which is configured to receive and discharge exhaust gases containing VOCs, in particular to the first heat treatment device. For example, the second heat treatment is carried out at a temperature above room temperature, in particular at a temperature below or equal to the boiling point of water, i.e. below or equal to 100°C, without pressurization. The elevated temperature allows a better release of VOCs from the wood chips. In particular, the exhaust gases containing VOCs are discharged from the second heat treatment device and / or guided into the first heat treatment device. Furthermore, exhaust gases containing VOCs from devices subsequently used to carry out the method can be fed into the second heat treatment device in order to further heat the wood chips or release VOCs.

[0082] As an example and independently of other features, the second heat treatment of the wood chips in the second heat treatment device can be carried out using steam, preferably water vapor. Here, a portion of the VOCs can be transferred from the wood chips into the steam. This steam containing VOCs can be discharged from the second heat treatment device, preferably from an upper portion thereof, and for example via a line arranged on top. Alternatively or in addition to discharging the steam containing VOCs, some or all of the steam can condense and release the VOCs from the wood chips as a condensate. This condensate containing VOCs can for example be guided into the compaction screw, the digester and / or the water treatment plant.

[0083] In particular, the third heat treatment step 50 can be carried out in a so-called digester. For example, at a temperature above room temperature, in particular at between 3 bar and 15 bar, including the end values, preferably between 5 bar and 13 bar, including the end values, preferably at 9 bar, at a temperature above the boiling point of water, i.e. 100°C, such as at 90°C to 175°C, wood chip digestion is carried out in a digester, which can be configured to receive and discharge exhaust gases containing VOCs. The elevated temperature allows for a better release of VOCs from the wood chips. The cleaning of the wood chips is preferably carried out with a water-containing medium, in particular a water-based medium. The first and second heat treatments have already heated and softened the wood chips, so that the VOCs contained in the wood chips are released from the digester with high efficiency. Preferably, a droplet separator is connected downstream of the digester.

[0084] It is an advantageous option that the compaction screw upstream of the digester and / or the digester itself receives the aforementioned condensate containing VOCs from the second heat treatment device. This condensate containing VOCs can be discharged from the processing system via the compaction screw and / or via the digester together with the VOCs optionally released during the digestion.

[0085] Subsequently, the wood chips are chopped in a refiner in a chopping or fiber separation step 60. The configuration and operation of the refiner can be adapted to the desired field of application of the board. In principle, a grinding energy of 50 to 200 kWh per ton of wood chips can be introduced via grinding tools, which are part of the refiner and perform the fiber separation on the wood chips. A lower grinding energy, such as about 50 kWh per ton of wood chips, is suitable for floor coverings, 150 kWh per ton of wood chips for high-quality furniture.

[0086] From the refiner, the fiber-separated wood chips or wood fibers obtained in this way are guided through a so-called blow line and, in a dryer, a drying step 70 for drying the wood fibers from the refiner is carried out. This can also be carried out at elevated temperatures, wherein the resulting moist atmosphere can be removed from the wood fibers by a separation step 80. For example, the exhaust air can be washed, so that last components, in particular VOC-containing components, can be washed out and possibly reused or collected.

[0087] The dried, fiber-separated wood chips or wood fibers obtained in this way are processed into fiber boards in a processing step 90. To this end, the fiber-separated wood chips can be glued and the glued, fiber-separated wood chips can be pressed into boards. Subsequently, the boards are subjected to a final processing for a specific application.

[0088] In the process described herein, vapors are produced or additional vapors are supplied. In order to advantageously remove VOCs produced from the raw wood material during the process, it is provided that vapors used or produced in the process are continuously separated from the process at at least one vapor discharge location, wherein the separated vapors are in a predetermined content range, such that the lower and upper limits of the total separated content of vapors depend on at least one specification of the wood chips used in process step a).

[0089] Thus, the separation of vapors for the removal of VOCs depends on the VOCs introduced into the process by the wood chips or their wood material. This can be considered, for example, with regard to the content and / or type of the wood material introduced or, in particular, with regard to the content of the VOCs introduced. In particular, the total content of the separated vapors can be in the range of 0.5 to 100 times the mass, preferably 0.5 to 50 times the mass, more preferably 0.5 to 10 times the mass, based on the terpene content of the wood chips provided. Alternatively or additionally, the total content of the separated vapors can be in the range of 0.001 to 0.2 times the mass, 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.

[0090] Various vapor discharge locations can be used to separate the vapors and thus remove the VOCs. In particular, a vapor discharge location is understood to be a location from which vapors can be separated from the process.

[0091] For example, the following vapor discharge locations are suitable for separating the vapors: the pre-pre-vapor container or the first heat treatment device, the pre-vapor container or the second heat treatment device, the digester or the third heat treatment device, or the refiner. Conveying units, such as screws or conveying devices, are also suitable, such as after the first heat treatment device, between the second heat treatment device and the third heat treatment device; or conveying units, such as screws, between the third heat treatment device and the refiner. Dehydration units are also suitable, such as dehydration screws, or vapor recirculation between separate process units.

[0092] However, it has been found that the following gas discharge locations are particularly suitable.

[0093] For example, the at least one gas discharge location can be positioned upstream of the refiner. Locations in this regard include, for example, the heat treatment device or a location in the vapor recirculation between the refiner and the heat treatment device, the vapor treatment device before the wood chip digester or the wood chip digester itself, or the vapor recirculation between the vapor treatment device and the digester.

[0094] Alternatively or additionally, it can be advantageous that the at least one vapour discharge location is positioned downstream of the refiner. In this regard, it is advantageous that the vapour discharge location positioned downstream of the refiner is a vapour separator positioned downstream of the refiner.

[0095] Further, it can be particularly preferred that the at least one vapour discharge location results from a liquid flow. Examples include an extrusion water flow directly from the compaction screw or a liquid flow emerging from the extrusion water flow of the compaction screw.

[0096] The method described herein enables a cost- and resource-saving method for reducing VOC emissions in the production of fibre boards, in particular HDF or MDF boards.

[0097] List of reference signs

[0098] 10 Step of providing wood chips

[0099] 20 First heat treatment step

[0100] 30 Cleaning step

[0101] 40 Second heat treatment step

[0102] 50 Third heat treatment step

[0103] 60 Chopping step

[0104] 70 Drying step

[0105] 80 Separation step

[0106] 90 Processing step.

Claims

1. A method for manufacturing fiber boards with reduced VOC emissions, wherein the method comprises at least the following method steps: a) providing wood-containing chips; b) heat-treating the chips in one heat-treatment device or in multiple heat-treatment devices; c) chopping the chips in a refiner; d) gluing the chips; and e) pressing the glued chips to form the fiber boards, wherein f) continuously separating steam used or produced in the method in a controlled manner from the method at at least one steam discharge location, wherein the steam is separated in a predetermined content range, such that the lower and upper limit of the content range of the total separated steam depends on at least one specification of the chips used in method step a), wherein depending on the content of the chips provided in method step a), the lower and upper limit of the content range of the total separated steam is in the range of 0.001 to 0.2 times the dry mass of the chips used in method step a), depending on the content of VOCs or terpenes contained in the chips provided in method step a), the lower and upper limit of the content range of the total separated steam is in the range of 0.5 to 100 times the content of VOCs or terpenes contained in the chips used in method step a).

2. The method of claim 1, wherein, The content of VOCs or terpenes contained in the chips used in method step a) is determined by examination of the chips used or is estimated based on the type of chips used.

3. The method according to any one of claims 1 or 2, characterized in that, In method step f), the total content of separated steam is in a content range of 0.5 to 50 times the VOC content of the chips based on the VOC content of the chips provided.

4. The method of claim 3, wherein, In method step f), the total content of separated steam is in a content range of 0.5 to 10 times the VOC content of the chips based on the VOC content of the chips provided.

5. The method according to any one of claims 1 or 2, characterized in that, In method step f), the total content of separated steam is in a content range of 0.001 to 0.1 times the dry mass of the chips based on the dry mass of the chips provided.

6. The method of claim 5, wherein, In method step f), the total content of separated steam is in a content range of 0.001 to 0.02 times the dry mass of the chips based on the dry mass of the chips provided.

7. The method of any one of claims 1 or 2, wherein, The at least one steam discharge location is positioned upstream of the refiner.

8. The method of claim 7, wherein, The steam discharge location positioned upstream of the refiner comprises a position at a heat-treatment device or between the refiner and a heat-treatment device.

9. The method of claim 7, wherein, The steam discharge location positioned upstream of the refiner is a position at a steam treatment device before a chip digester or at the chip digester itself or between the steam treatment device and the chip digester.

10. The method of any one of claims 1 or 2, wherein, The at least one steam discharge location is positioned downstream of the refiner.

11. The method of claim 10, wherein, A steam separator is positioned downstream of the refiner.

12. The method of any one of claims 1 or 2, wherein, The at least one steam discharge location results from a liquid flow.

13. The method of claim 12, wherein, The liquid flow is an extrusion water flow directly from a compaction screw or a liquid flow emerging from an extrusion water flow from a compaction screw.

14. The method of any one of claims 1 or 2, characterized in that, The VOC-containing steam removed according to method step f) is collected and one or more components are further processed.

15. The method of claim 14, wherein, As further processing, a terpene or turpentine mixture is separated.

16. The method of claim 14, wherein, As further processing, a hydrosol is separated.

17. The method of claim 14, wherein, The separated vapors or one or more components are further treated by combustion or exposure to high temperatures, adsorption, absorption, membrane technology, condensation, crystallization, or other suitable process engineering techniques.

18. The method of any one of claims 1 or 2, wherein, The heat of the material streams produced in the process is used in the process in an energetic manner.

19. The method of any one of claims 1 or 2, wherein, The heat of the separated vapor stream is used in the process in an energetic manner.

20. The method of any one of claims 1 or 2, wherein, The process is a thermomechanical process for the production of MDF boards or HDF boards. The process is a thermomechanical process for the production of MDF boards or HDF boards.

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