EP4122662B1 - Method for producing fibreboard with reduced voc emissions - Google Patents

Description

The invention relates to a method for producing fiberboard with reduced VOC emissions, in particular for producing HDF boards or MDF boards.

A continuous production process of wood fibers using the dry and wet method, based on lignocellulose-containing material such as wood, straw or bagasse, includes, among other things, shredding the raw material into free fibers or fiber aggregates, which in subsequent steps are coated with adhesive, dried, shaped and formed into one The end product, the so-called board or wood fiber board, is pressed. Today, the release of fibers from the raw material preferably takes place in a so-called thermomechanical process in one step or in a thermal and mechanical process in at least two separate steps.

Before the first thermal treatment, the wood chips are usually washed to remove dirt such as soil or stones. The thermal treatment, i.e. the heating of the raw material, takes place, among other things, in a first thermal treatment device at a preferred temperature of up to approximately 100 degrees Celsius, in particular under atmospheric pressure, and then in a preferably pressurized second thermal treatment device at a temperature of, for example, approximately 150 up to 190 degrees Celsius, especially under a pressure of around 4 to 13 bar. The residence time of the wood chips in the thermal treatment devices can be adjusted depending on the prevailing process conditions and can be between approximately 1 and 10 minutes, for example. According to the prior art, the thermal heating in the second thermal treatment device is preferably carried out using steam. The mechanical processing then takes place in what is also known as a defiberer Refiner. The residence time of the wood chip raw material in the refiner is short. The energy converted into mechanical energy associated with mechanical processing is converted into heat in the reduction zone and appears as exhaust gas, especially steam, in the processing system, which is generated from the moisture in the raw material.

After defibration in the refiner, the wood fibers are usually transported pneumatically to a fiber dryer, where the drying process is carried out with a large amount of air and a controlled inlet air temperature of around 140 to 200 degrees Celsius, depending on the current fiber moisture. The fibers are mechanically separated from the drying air. The dried fibers are then transported further for forming, pre-pressing and finally final pressing of the board. The drying air is subjected to exhaust gas scrubbing. Wet washing, wet electrostatic precipitators or biofilters and biological wastewater treatment are used for this purpose.

According to the prior art, the wood emissions released during the release of the fibers and drying, especially in the second thermal treatment device, are transported from the first thermal treatment device via the refiner together with the fiber bulk material to the dryer, where the majority is separated from the fiber and finally moist drying air from the dryer is released into the atmosphere after the exhaust gas scrubbing. These wood emissions mainly contain volatile organic substances, so-called volatile organic compounds (VOCs).

Among the VOCs, there are substances whose solubility in water during wet exhaust gas scrubbing is so low that their separation efficiency is only a small percentage or even approaches zero. This particularly applies to terpenes. It is therefore known that wet deposition processes only achieve an emission reduction of 10-30%. The low solubility is due, on the one hand, to the inherently low solubility of the substances in water, and, on the other hand, to the strong dilution in the drying air, which extremely reduces the partial pressure and thus the thermodynamic driving force. The terpenes come from the resin of the wood used. These are highly volatile oils. They are also known as turpentine.

The remaining quantities that do not leave the dryer follow the fiber flow to the subsequent process units, where they are successively released into the surrounding atmosphere or appear as a residual product in the final product, the plate. This means that emissions can also be discharged into the atmosphere from the end product.

From the WO 99/10594 It is previously known that the second thermal treatment device is equipped with an upper outlet for degassing the organic emissions released there. Here the steam is introduced in the lower part of the first thermal treatment device and the wood chips that penetrate into the upper part of the first thermal treatment device are washed in the countercurrent steam during the condensation of the steam. This is achieved by the steam moving up through the wood chip column to the colder wood chips in the upper part of the first thermal treatment device. The released emissions, exhaust air and steam resulting from the evaporation of moisture in the wood chips are separated and disposed of through the outlet in an appropriate device. It is also known from this publication that the wood chips are transported from the first thermal treatment device into the refiner by means of a screw conveyor, which compresses and dewaters the wood chips during transport.

According to the disclosure document EP 1597427 A1 A method is known in which the exhaust gases produced during compression are disposed of in a screw conveyor via an outlet arranged in the compression zone. The system according to this document is characterized in that an exhaust gas outlet is arranged in the compression zone for the removal of evaporated moisture, which is produced when the wood chips are compressed and contains exhaust gases containing VOCs.

EP 2 573 258 A1 describes a method and a device for processing wood chips for the production of wood-containing pulp. With regard to washing the wood chips, it is stated that this is done by heating up to around 90°C with water heated to up to 98°C.

US 4,925,527 describes a process for obtaining turpentine from a TMP (thermal mechanical pulp) process in which a gas stream is removed from a refiner and fed to a condenser.

EP 1 021 612 A1 describes a system for the production and treatment of wood fibers, consisting of a fiber-producing part that is connected to a wood chip preheater and a beater, which serves to free the fibers from the wood chips, and at least one dryer stage, which serves to dry the fibers. Between the fiber producing part and the dryer stage, a steam separator part is provided, which includes a cyclone separator, the inlet of which is connected to the blower line used for the fibers and the steam obtained from the beating machine. The lower outlet of the cyclone separator is connected to a conveying/drying line for the fibers via a sluice gate. The upper outlet of the cyclone separator is connected to devices designed to separate volatile organic substances and recover heat from the steam from the cyclone separator.

US 2012/227918 A1 describes a vapor separation system for refiners comprising a blow line for transporting a fiber material mixture from a refiner to an inlet of a vapor separator. The exhaust steam is discharged from the separator through an exhaust steam outlet. Cleaned fiber material is discharged from the separator through an outlet that prevents a significant portion of the exhaust vapor from passing through the outlet. A relay tube communicates with the outlet and a dryer duct and transports the cleaned fiber material between the two. A resin inlet communicates with and supplies resin into the relay tube. The resin is mixed with the cleaned fiber material before the cleaned fiber material is dried in the dryer channel.

However, in the interests of environmentally friendly wood processing, there is a need to remove the VOCs even more efficiently from a process for producing fiberboard, in particular for producing HDF boards or MDF boards, and in particular a resource-saving process should also be made possible.

The object is achieved according to the invention by a method for producing fiberboard with reduced VOC emissions with the features of claim 1. Preferred embodiments of the invention are specified in the subclaims and the following description, each of which individually or in combination represents an aspect of the invention can.

1. a) Bereitstellen von holzhaltigen Hackschnitzeln;
2. b) Thermisches Behandeln der Hackschnitzel in einer thermischen Behandlungsvorrichtung oder in einer Mehrzahl an thermischen Behandlungsvorrichtungen;
3. c) Zerkleinern, insbesondere Zerfasern der Hackschnitzel in einem Refiner;
4. d) Beleimen der zerkleinerten, insbesondere zerfaserten Hackschnitzel; und
5. e) Pressen der zerkleinerten, insbesondere zerfaserten und beleimten Hackschnitzel zum Ausformen der Faserplatte,
   wobei
6. f) in dem Verfahren verwendeter oder entstehender Dampf an wenigstens einer Dampf-Emissionsstelle insbesondere kontinuierlich aus dem Verfahren kontrolliert abgetrennt wird, wobei der Dampf in einem vorgegebenen Mengenbereich abgetrennt wird derart, dass eine Untergrenze und eine Obergrenze des Mengenbereichs des gesamt abgetrennten Dampfes in Abhängigkeit wenigstens einer Spezifikation der in Verfahrensschritt a) eingesetzten Hackschnitzel erfolgt.

A process for producing fiberboard with reduced VOC emissions is described, the process having at least the following process steps:

1. a) Providing wood chips containing wood;
2. b) thermally treating the wood chips in a thermal treatment device or in a plurality of thermal treatment devices;
3. c) comminution, in particular defibration, of the wood chips in a refiner;
4. d) gluing the shredded, especially defibered, wood chips; and
5. e) pressing the shredded, especially fiberized and glued wood chips to form the fiberboard,
   where
6. f) steam used or generated in the process is separated from the process in a particularly continuous, controlled manner at at least one steam emission point, the steam being separated in a predetermined quantity range in such a way that a lower limit and an upper limit of the quantity range of the total separated steam are dependent on at least a specification of the wood chips used in process step a).

Such a process makes it possible to efficiently reduce environmentally harmful VOC emissions in the production of fiberboard in a particularly advantageous manner. A resource-saving process is also possible.

For the purposes of the present invention, the term VOC (Volatile Organic Compounds) refers in particular to those volatile compounds that are present in the wood that serves as the starting material for the process described here. In particular, the VOCs described in this process are terpenes, which occur as wood oil in the wood. Examples include the following substances, which can occur in the weight percentages given 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%). Other components may include myrcene, α-, β-phellandrene, 3-carene, cymol/cymene, terpinols, ocimene.

The term “controlled” in the sense of the present invention means, with regard to the separation of the steam, that the amount and/or the material flow of the steam to be separated is adjustable, preferably controllable. In this respect, non-adjustable and/or non-controllable vapor emission points are not to be understood as a controlled separation of the vapor within the meaning of the invention.

The process described here is used to produce fiberboard. For the purposes of the present invention, fiberboard is to be understood, in a manner known per se, as boards which have wood fibers in a matrix made of a binder. For example, the fiberboards can include so-called medium-density fiberboards (MDF boards, density for example 700-800 kg/m ³ ) or low-density fiberboards (LDF, density for example <650 kg/m ³ ). Furthermore, so-called high-density fiberboards (HDF boards, density, for example > 800 kg/m ³ ) can be produced using the method described. Particularly preferably, MDF boards or HDF boards can be produced using the process described. Such fiberboards are particularly suitable for interior house construction as sub-covering panels for roofs or external paneling for walls. The panels are also used in a variety of ways in furniture construction. It is also suitable for use as floor, ceiling or wall coverings for the interior design of rooms.

First, in the method described here, wood chips containing wood are provided in accordance with method step a). In principle, any wood can be provided in this step, which is roughly chopped so that it can be provided as wood chips.

The wood used is not fundamentally limited, for example, wood selected from pine wood, spruce wood, lark wood, birch wood, beech wood, dead oak wood, alder wood, etc. can be used, but is not limited to this.

The raw wood can be processed into wood chips, for example, by roughly chopping the wood used as the starting material and then debarking it and cleaning it from coarse impurities, for example by removing sand components or stones. The size of the wood chips is not fundamentally limited, as is generally known to those skilled in the art from the production of fiberboard.

According to method step b), the method includes thermally treating the wood chips in a thermal treatment device or in a plurality of thermal treatment devices. In this process step, the wood chips can be processed in particular with steam or with hot water under pressure, for example in order to remove VOCs from the wood. Accordingly, the temperature in this process step can be at least partially in a range of above 100 ° C. In addition, the can thermal treatment or can the thermal treatments serve to further purify the wood chips.

According to process step c), the wood chips are comminuted in a refiner. In this process step, the previously roughly chopped wood is further chopped so that it takes on the shape that is suitable for the panels to be produced. This can be adjusted, for example, by adjusting the grinder or the energy thereby introduced into the wood chips and/or the duration of the treatment of the wood chips, as is generally known to those skilled in the art. In particular, the wood chips can be defibered in this process step.

The comminuted or fiberized wood chips obtained after process step c) are then glued according to process step d). Gluing is understood to mean, in particular, the introduction of the wood chips into a matrix of binders that serve 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 the binder is preferably hardenable, for example using heat, so that after hardening a stable structure is created, which can serve as a corresponding fiberboard.

Accordingly, the fiberized and glued wood chips can then be pressed according to process step e) to form a fiberboard, in particular using heat and / or electromagnetic radiation. In an understandable manner, the specific parameters to be used in this process step depend on the materials to be pressed, in particular on the glue or binder used.

In the method described here, it is further provided that, according to method step f), steam used or produced in the method is separated from the method in a controlled manner at at least one steam emission point, the vapor being separated in a predetermined quantity range in such a way that a lower limit and an upper limit of the quantity range of the total separated steam depends on at least one specification of the wood chips used in process step a). The separation of the steam can preferably take place continuously. A continuous separation of the steam includes, for example, an uninterrupted separation or a constant periodic separation, i.e. comprehensively definable periodically recurring breaks.

In particular, in that steam used or generated in the process is separated from the process in a controlled manner at at least one steam emission point, the steam being separated in a predetermined quantitative range in such a way that a lower limit and an upper limit of the quantitative range of the total separated steam depending on at least a specification of the wood chips used in process step a) takes place, significant advantages can be achieved compared to the solutions from the prior art.

The invention is based in particular on the fact that by separating steam from the process, VOCs can be separated from the production stream, since they accumulate in the steam. Appropriate vapor separation thus reduces the emission of VOCs, for example as exhaust gases or as vapors from the manufactured product, i.e. the fiberboard produced.

Surprisingly, it has been shown that it is not necessary to continuously separate large amounts of steam from the process in order to achieve a significant reduction in VOC emissions. Rather, it was found that almost the entire amount of VOCs, especially terpenes, can be removed by emitting comparatively small amounts of vapor. As a result, the amount of steam discharged and thus, for example, the amount of steam to be further processed can be significantly reduced. This allows the effort and costs of the overall process to be reduced.

In addition, when producing fiberboard, it is often necessary to generate additional steam in addition to the steam that is generated during the process in order to obtain a sufficient amount of steam for the corresponding processing steps. However, the generation of steam also involves effort and costs, which can be significantly reduced according to the invention.

The process described here also takes advantage of the fact that terpenes, the most important VOCs in this process, have a boiling point of over 150 ° C, but it was still found that even exhaust steam streams or steam streams in general with temperatures of below 100 ° C contain a significant amount of volatiles organic substances and in particular may contain terpenes. It is therefore advantageous in the method described here that the total amount of steam separated is taken into account, regardless of its origin or the local separation point.

The separation of steam streams can in principle be carried out using methods from the prior art and it is advantageous that the steam is treated to collect the VOCs and is not immediately released into the environment along with the VOCs. For example, the steam can be separated using excess pressure or negative pressure.

The fact that the steam is separated in a predetermined quantity range in such a way that a lower limit and an upper limit of the quantity range of the total separated steam takes place depending on at least one specification of the wood chips used in process step a) can be implemented in a variety of ways, as will be done in greater detail below is described in detail.

Following the process described here, the fiberboards produced can be further processed, particularly depending on their specific area of application. For example, the fiberboards produced can be sanded, sawn into smaller plates, or further layers can be applied, for example in lamination processes. Furthermore, it is possible to introduce certain structures into the plates, which can be used to attach them to one another or to other substrates. This allows the fiberboard to be advantageously used for the desired application.

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

For example, one or a plurality of specifications may be selected from the following specifications.

In particular, a specification can be the amount of wood chips used in the process. The amount of both wood chips and steam can be the absolute amount in a batch process, or can be the amount of both wood chips and steam of steam in a continuous process can be the amount per unit of time. It is understandable that, regardless of the specific design and components of the wood chips, the amount of wood chips has a significant influence on the VOCs introduced into the process by the wood and thus also on the VOCs to be discharged, so that the amount of wood chips in the determination the amount of steam to be separated should preferably be taken into account.

Alternatively or preferably in addition to the amount of wood chips used, it may be preferred that a lower limit and an upper limit of the quantitative range depend on the amount of VOCs contained in the wood chips provided in process step a), in particular the terpenes contained. In particular, it can be determined or estimated how much VOC and thus in particular how much terpenes occurring in wood are contained in the wood chips per amount of wood chips. In other words, the amount of terpenes or VOCs in weight percent, based on the amount of wood chips, that occur in the wood chips can be taken into account.

This specification can be particularly advantageous because it has been shown that different types of wood also have different amounts of terpenes. Accordingly, the amount of VOCs present in a certain amount of wood chips can depend on the specific type of wood used.

In particular, by selecting such specifications, the amount of steam to be separated can be reduced particularly reliably, since it is ensured that fluctuations in the VOCs that occur when separating the steam do not result in too little steam being separated and thus an undesirably high content of VOCs emerging. In addition, the amount of steam to be separated and produced can still be safely reduced reliably and without the danger described above.

It can also be advantageous if the amount of VOCs contained in the wood chips used in process step a), in particular the terpenes contained, is determined by examining the wood chips used or is estimated based on the type of wood chips used.

Determining the amount of VOCs by examining the wood chips can enable a particularly precise determination of the VOCs contained in the wood chips, see above that the determination of the amount of steam to be separated can also be carried out very precisely. The amount of VOC can be determined in a manner known per se by analyzing the components of the wood chips. This can be advantageous, for example, because the VOC content can be reduced simply due to evaporation during storage or fluctuations in the VOCs contained in the same type of wood can occur.

An estimation of the VOCs contained in the wood chips, in particular the amount of terpenes contained, based on the type of wood chips used, i.e. in particular by considering what type of wood the wood chips are made from, can allow a particularly simple determination of the amount of VOCs, although the effort is very high can be kept low. This embodiment can be based in particular on the fact that different types of wood, for example birch or spruce, often have a different amount of VOC such as terpenes, but the amount of VOC contained and in particular the amount of terpene is characteristic of the type of wood. This means that the amount of VOC can be estimated in advance by knowing the wood used, without having to carry out any analysis.

To ensure that potentially occurring inaccuracies in the amount of VOC in the respective wood are not critical, the amount of vapor separated can be determined with a definable safety factor, i.e. a definably larger amount of vapor can be separated than is necessary according to the terpene amount data used. This also allows a particularly safe and reliable reduction in the amount of VOCs discharged from the process.

It has been found that it is already sufficient if the total amount of steam separated off in process step f) is in a quantity range of 0.5 to 100 times the mass, preferably 0.5 to 50 times the mass, particularly preferably 0 .5 to 10 times the mass based on the amount of terpenes in the wood chips provided. This amount is significantly below the amount of steam contained in solutions from the prior art, for example in US 4,925,527 , is separated, however, is surprisingly sufficient to remove essentially the entire amount of VOCs from the process and thus significantly reduce the VOC emissions in the process for producing fiberboards described here. It has therefore been shown that, for example, when the process described here or the amount of steam separated in the process is based on the amount of VOCs such as terpenes introduced into the process by the wood chips, a surprising result small amount of steam can be separated, which is sufficient to solve the problem according to the invention.

Alternatively or additionally, the dry mass of the wood chips provided can also be a good indicator for determining the amount of steam to be separated. It can be advantageous if the total amount of steam separated off in process step f) is in a quantity range of 0.001 to 0.2 times the mass, preferably 0.001 to 0.1 times the mass, particularly preferably 0.001 to 0.02 -fold mass based on the dry mass of the wood chips provided.

Even with such a correlation, the amount of vapor to be separated is significantly below the amount found in solutions from the prior art, for example US 4,925,527 is separated, however, is also surprisingly sufficient to remove almost the entire amount of VOCs from the process and thus significantly reduce the VOC emissions in the process for producing fiberboard described here. It has therefore been shown that, for example, even if the method described here or the amount of steam separated in the method is based on the dry mass of the wood chips provided, a surprisingly small amount of steam can be separated, which is sufficient to solve the problem according to the invention.

The dry matter of the wood or wood chips refers in particular to absolutely dry wood (atro), as is common in wood processing. The dry matter of wood used can in turn be determined analytically or estimated based on known data for the type of wood used. In addition, the mass can be easily determined in continuous or batch processes, as an amount per unit of time or as an absolute amount, as described above.

It has also been shown that it is advantageous for at least one steam emission point to be positioned upstream, i.e. in front of the refiner in terms of process technology. It has been shown that a significant amount of VOCs are removed from the wood before the refiner and it is therefore advantageous to remove the VOCs from the process by steam separation before the refiner. On the one hand, this allows effective VOC removal to be achieved. In addition, the VOCs can be prevented from being carried along in the process, which may make removal more difficult.

With regard to positioning upstream of the refiner, it may be of particular advantage for the steam emission point positioned upstream of the refiner to comprise a thermal treatment device or to be positioned between the refiner and a thermal treatment device, such as a digester. It has been shown that, particularly at these positions, VOCs, such as terpenes in particular, can be effectively removed from the process by vapor separation, so that the process can be carried out particularly effectively in this embodiment.

Accordingly, it can also be advantageous for the steam emission point to be a steam treatment device in front of a 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 and especially terpenes can be effectively removed from the process at these emission points.

A vapor separation upstream of a position, such as the refiner, can be a position on the main material stream of the wood chips or a vapor return, which runs in the opposite direction to the main material flow but is still adjacent to the corresponding position of the Main material flow or due to the course of the vapor recirculation can be described as upstream. Thus, for example, a vapor return from the refiner to a thermal treatment device is to be viewed as upstream of the refiner.

As described above, it can be very effective to separate the vapor at one or more vapor emission points upstream of the refiner. In particular, since the process described here is characterized by the fact that only a very reduced amount of steam is separated, it can be advantageous, if at least, in order to enable particularly effective steam separation and to completely remove the VOCs from the process a steam emission point is positioned downstream of the refiner. This configuration therefore makes it possible, even if not all terpenes are removed upstream of the refiner, to drive them out of the process downstream of the refiner.

Particularly in this embodiment, a reduction in VOC emissions can be reduced particularly effectively.

With regard to an effective reduction of VOC emissions, it can be particularly advantageous for the steam emission point positioned downstream of the refiner to be a steam separator positioned downstream of the refiner. A steam separator is to be understood as a device in which steam is to be removed from the process. In addition to an effective VOC reduction, this design can also be implemented without a lot of equipment.

It may further be preferred that at least one vapor emission point is generated from a liquid stream. In this embodiment, steam can emerge from a correspondingly hot liquid stream, which is then separated, or a cooler liquid stream, from which no steam emerges, can be heated until steam emerges in order to separate the steam streams generated in this way.

In this embodiment, it can be taken into account that VOCs or terpenes that have escaped from the wood do not only accumulate in the vapor but can also be found in liquid streams, at least in small quantities. By vapor emission from these liquid streams, such proportions of VOCs can then be effectively removed from the process, which can further make the reduction of VOCs as a whole more effective.

Examples of liquid streams in which VOCs could be found include, for example, a squeezed water stream directly from a stuffing screw or a liquid stream resulting from a squeezed water stream from a stuffing screw.

It can also be advantageous to collect the VOC-containing vapor removed according to process step g) and, if necessary, to further treat one or more components. In this embodiment, the process can not only serve to reduce VOC emissions, but the process can be carried out much more economically due to the possibility of collecting separated vapor streams and, if necessary, treating them further. This is because the materials contained in the steam stream or other properties of the steam stream, such as its heat, can be used in the process or other processes so that costs and resources can be saved.

For example, it may be advantageous to isolate a mixture of terpenes or turpentine oil as further treatment. Such substances should be considered emissions from the process for the manufacture of fiberboard to prevent release into the environment, however these substances may be valuable products for other processes or applications. This configuration can therefore be particularly advantageous in terms of the economics of the process described here and in terms of the added value of the wood used. The same applies if, for example, a hydrosol is isolated for further treatment. For the purposes of the invention, hydrosol is generally understood to mean the aqueous phase obtained after condensation of the vapor, which may contain corresponding water-soluble components, such as formaldehyde.

It can also be advantageous for the separated vapor or one or more components to be further treated by combustion or exposure to high temperatures, adsorption, absorption, membrane technology methods, condensation, crystallization or other suitable process engineering methods.

Burning or exposing to high temperatures enables, for example, thermal afterburning and thereby energetic use of the VOCs contained in the separated steam stream. The other methods mentioned can all relate to the isolation or separation of individual substances.

It can also be advantageous for the heat of a material stream occurring in the process, for example a separated steam stream, to be used further energetically in the process. In this embodiment, the energy inherent in the material flow can be further used in the form of heat, in particular to heat other material flows. This step can also improve economic aspects of the method according to the invention and thus save costs and resources.

Fig. 1

eine schematische Darstellung eines Verfahrens gemäß der vorliegenden Erfindung.

The invention is explained below by way of example with reference to the accompanying drawings using preferred exemplary embodiments, whereby the features shown below can represent an aspect of the invention both individually and in combination. It shows:

Fig. 1

a schematic representation of a method according to the present invention.

In Figure 1 a method according to the present invention is shown schematically. Solid arrows should indicate the main material flow and dash-dotted arrows should show vapor recirculation.

At step 10, wood chips are provided. These are made from a fundamentally selectable wood and are provided by roughly reducing the size of the wood and in particular by coarsely washing it.

The wood chips are then treated in a number of thermal treatment devices. This is realized in a first thermal treatment step 20, in a second thermal treatment step 40 and in a third thermal treatment step 50.

Basically, in the sense of the invention it is provided that VOC-containing exhaust gases have a high temperature. This means in particular a temperature greater than the boiling point of water, i.e. 100 ° C, so that this temperature can also be present at least partially during the thermal treatment.

The first thermal treatment step 20 takes place in a so-called pre-steam vessel at a preferred temperature of up to approximately 100 ° C, in particular under atmospheric pressure. This is a first thermal treatment of the wood chips and is carried out using steam, preferably water vapor. Some of the VOCs can transfer from the wood chips to the steam. This VOC-containing steam can be discharged from the first thermal treatment device at a steam emission point, preferably from its upper section and, for example, via a pipeline arranged on the roof.

The wood chips are then washed or cleaned in a cleaning step 30 before the second thermal treatment step 40. The wood chips are cleaned in a washing device in particular at a temperature above room temperature and less than or equal to the boiling temperature of water, in particular between 80 ° and 100 ° C. An increased temperature enables better separation of wood chips and foreign matter. This means that foreign substances that are not wood chips are filtered out and removed from the processing system. The wood chips are preferably cleaned with a water-containing, in particular water-based, medium.

It is an advantageous option for the washing device to absorb the aforementioned VOC-containing condensate from the first thermal treatment device. This VOC-containing condensate can be removed from the processing system along with VOC released during washing.

The second thermal treatment step 40 of the wood chips takes place in the second thermal treatment device, also called a pre-steam tank, which is designed to absorb and eliminate VOC-containing exhaust gases, in particular back into the first thermal treatment device. The second thermal treatment takes place, for example, without pressure at a temperature above room temperature, in particular at a temperature less than or equal to the boiling temperature of water, i.e. less than or equal to 100 ° C. Increased temperature allows for better release of VOCs from the wood chips. The VOC-containing exhaust gases are in particular removed from the second thermal treatment device and/or forwarded into the first thermal treatment device. Furthermore, VOC-containing exhaust gases from a device subsequently used to carry out the method can be fed into the second thermal treatment device in order to further heat the wood chips or to release VOCs.

By way of example and independently of other features, it is possible for the second thermal treatment of the wood chips to take place in the second thermal treatment device using steam, preferably water vapor. Some of the VOCs can transfer from the wood chips to the steam. This VOC-containing steam can be removed from the second thermal treatment device, preferably from its upper section and, for example, via a pipeline arranged on the roof. Alternatively or in addition to removing the VOC-containing vapor, some or all of the vapor can condense and release VOCs from the wood chips as condensate. This VOC-containing condensate can, for example, be passed on to a stuffing screw and/or a cooker and/or to a water treatment system.

The third thermal treatment step 50 can take place in particular in a so-called cooker. The cooking of the wood chips in the cooker, which can be designed to absorb and eliminate VOC-containing exhaust gases, takes place, 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 9 bar, at a temperature greater than the boiling point of water, i.e. 100 °C, approximately 90-175 °C. Increased temperature allows for better release of VOCs from the wood chips. The wood chips are preferably cleaned with a water-containing, in particular water-based, medium. The first and second thermal treatments have heated and softened the wood chips such that VOCs contained in the wood chips are efficiently released from the digester. A mist separator is preferably connected downstream of the cooker.

It is an advantageous option for a stuffing screw upstream of the cooker and/or the cooker to absorb the aforementioned VOC-containing condensate from the second thermal treatment device. This VOC-containing condensate can be removed from the processing system via the stuffing screw and/or via the cooker together with optional VOC released during cooking.

The wood chips are then shredded in a shredding step 60 or defibration step in the refiner. The design and operation of the refiner can be adapted to the desired area of application of the plate. In principle, a grinding energy of 50 - 200 kWh/t of wood chips can be introduced via the grinding tools, which are part of the refiner and defibrate the wood chips. Lower grinding energy in the range of 50 kWh/t wood chips is suitable for floor coverings, while 150 kWh/t wood chips is suitable for high-quality furniture.

Starting from the refiner, the defiberized wood chips or the wood fibers obtained in this way are passed through a so-called blowline and a drying step 70 takes place in a dryer for drying the wood fibers coming from the refiner. This can in turn be done at elevated temperatures, whereby the resulting moist atmosphere can be removed from the wood fibers by a separation step 80. The exhaust air can, for example, be washed so that the final components, in particular components containing VOCs, can be washed out and, if necessary, further used or collected.

The dried defiberized wood chips or the wood fibers obtained in this way are processed into fiberboard in a processing step 90. For this purpose, the fiberized wood chips can be glued and the glued, fiberized wood chips can be pressed into a plate. The panel can then be finished for the specific application.

In the process described here, steam is created or additional steam is added. In order to advantageously remove the VOCs emerging from the raw wood during the course of the process from the process, it is provided that steam used or produced in the process is continuously separated from the process at at least one steam emission point, the steam being separated off in a predetermined quantity range is such that a lower limit and an upper limit of the quantitative range of the total separated steam is determined depending on at least one specification of the wood chips used in process step a).

The separation of the steam to remove VOCs thus takes place depending on the VOCs introduced into the process by the wood chips or their wood. This can be done, for example, taking into account the amount and/or type of wood brought in or specifically the amount of VOCs entered. In particular, the total amount of vapor separated can be in a range from 0.5 to 100 times the mass, preferably 0.5 to 50 times the mass, particularly preferably 0.5 to 10 times the mass, based on the amount of terpene provided wood chips. Alternatively or additionally, the total amount of steam separated off can be in a quantity range from 0.001 to 0.2 times the mass, preferably 0.001 to 0.1 times the mass, particularly preferably 0.001 to 0.02 times the mass, based on the dry mass of the wood chips provided.

Various steam emission points can be used to separate the steam and thus remove the VOCs. A steam emission point is to be understood in particular as a point at which steam can be separated from the process.

For example, the following steam emission points are suitable for separating steam, namely the pre-steam container or a first thermal treatment device, the pre-steam container or a second thermal treatment device, the cooker or the third thermal treatment device or the refiner. Furthermore, transport units such as a screw or conveyor units, such as after the first thermal treatment device, between the second and third thermal treatment devices, or a transport unit, such as a screw between the third thermal treatment device and the refiner, are suitable. There is also one Dewatering unit, such as a dewatering screw, is suitable or steam returns between individual processing units.

However, it has been found that the following gas emission points are particularly suitable.

For example, at least one gas emission point can be positioned upstream of the refiner. Relevant positions include, for example, a thermal treatment device or a position in a steam return between the refiner and a thermal treatment device, a steam treatment device in front of a wood chip cooker or the wood chip cooker itself, or a steam return between the steam treatment device and the cooker.

Alternatively or additionally, it may be advantageous for at least one steam emission point to be positioned downstream of the refiner. In this regard, it is advantageous that the steam emission point positioned downstream of the refiner is a steam separator positioned downstream of the refiner.

Furthermore, it may be particularly preferred that at least one vapor emission point is generated from a liquid stream. Examples include, for example, a squeezed water stream directly from a stuffing screw or a liquid stream resulting from a squeezed water stream from a stuffing screw.

The process described here allows a cost- and resource-saving way to reduce VOC emissions in the production of fiberboard, especially HDF or MDF boards.

Reference symbol list

10

Step of providing the wood chips

20

first thermal treatment step

30

Cleaning step

40

second thermal treatment step

50

third thermal treatment step

60

crushing step

70

drying step

80

Separation step

90

Processing step

Claims (20)

1. A process for manufacturing fiberboards with reduced VOC emissions, wherein the process includes at least the following process steps:

   a) providing wood-containing wood chips;

   b) thermally treating the wood chips in a thermal treatment device or in a plurality of thermal treatment devices;

   c) shredding the wood chips in a refiner;

   d) gluing the wood chips; and

   e) pressing the glued wood chips to form the fiberboard,
   wherein

   f) vapor used or arising in the process is separated continuously from the process at at least one vapor emission location in a controlled manner, wherein the vapor is separated in a predetermined quantity range such that a lower limit and an upper limit of the quantity range of the total separated vapor depend on at least one specification of the wood chips used in process step a).
2. The process according to claim 1, characterized in that a lower limit and an upper limit of the quantity range of the separated vapor depend on the quantity of wood chips provided in process step a).
3. The process according to claim 1 or 2, characterized in that a lower limit and an upper limit of the quantity range of the separated vapor depend on the quantity of VOCs, especially terpenes, contained in the wood chips provided in process step a).
4. The process according to claim 3, characterized in that the quantity of VOCs, especially terpenes, contained in the wood chips used in process step a) is determined by examining the wood chips used or is estimated based on the type of wood chips used.
5. The process according to any of claims 1 to 4, characterized in that the total separated quantity of vapor in process step f) is within a quantity range from 0.5 to 100 times the mass, preferably from 0.5 to 50 times the mass, more preferably from 0.5 to 10 times the mass, based on the VOC quantity of the wood chips provided.
6. The process according to any of claims 1 to 5, characterized in that the total separated quantity of vapor in process step f) is within a quantity range from 0.001 to 0.2 times the mass, preferably from 0.001 to 0.1 times the mass, more preferably from 0.001 to 0.02 times the mass, based on the dry mass of the wood chips provided.
7. The process according to any of claims 1 to 6, characterized in that at least one vapor emission location is positioned upstream of the refiner.
8. The process according to claim 7, characterized in that the vapor emission location positioned upstream of the refiner includes a thermal treatment device or is located between the refiner and a thermal treatment device.
9. The process according to claim 7 or 8, characterized in that the vapor emission location positioned upstream of the refiner is a vapor treatment device before a wood chip cooker or the wood chip cooker itself, or is located between the vapor treatment device and the cooker.
10. The process according to any of claims 1 to 9, characterized in that at least one vapor emission location is positioned downstream of the refiner.
11. The process according to claim 10, characterized in that the vapor emission location positioned downstream of the refiner is a vapor separator positioned downstream of the refiner.
12. The process according to any of claims 1 to 11, characterized in that at least one vapor emission location is generated from a liquid stream.
13. The process according to claim 12, characterized in that the liquid stream is a squeeze water stream directly from a compaction screw, or a liquid stream emerging from a squeeze water stream from a compaction screw.
14. The process according to any of claims 1 to 13, characterized in that the VOC-containing vapor removed according to process step f) is collected and, if applicable, one or more components are further treated.
15. The process according to claim 14, characterized in that, as further treatment, a mixture of terpenes or turpentine oil is isolated.
16. The process according to claim 14 or 15, characterized in that, as further treatment, a hydrolate is isolated.
17. The process according to any of claims 14 to 16, characterized in that 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.
18. The process according to any of claims 1 to 17, characterized in that the heat of a material stream occurring in the process is energetically reused in the process.
19. The process according to any of claims 1 to 18, characterized in that the heat of a separated vapor stream is energetically reused in the process.
20. The process according to any of claims 1 to 19, characterized in that the process is a thermomechanical process in which MDF boards or HDF boards are manufactured.

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