Process for producing a wood fibre material, and wood fibre material production device
Patent Information
- Application Number
- EP2024711243
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-23
- Filing Date
- 2024-03-19
- Publication Date
- 2026-01-28
AI Technical Summary
The existing wood pulp production methods are inefficient in terms of energy consumption and fail to effectively purify steam diverted after defibration, leading to accumulation of volatile organic substances like terpenes and aldehydes in the wood pulp, which is undesirable for producing wood fiber boards.
Introducing an oxidizing agent into the diverted steam to oxidize and purify it, allowing the cleaned steam to be reused for heating wood chips, thereby reducing energy consumption and preventing the accumulation of volatile organic substances in the wood pulp.
This approach reduces energy consumption in wood pulp production by utilizing purified steam and prevents the settlement of terpenes and aldehydes in the wood pulp, enhancing the quality of wood fiber boards like LDF, MDF, or HDF.
Smart Images
Figure EP2024057236_26092024_PF_FP
Abstract
Description
[0001] Method for producing a wood pulp and wood pulp producing device
[0002] The invention relates to a method for producing a wood fiber material, comprising the steps of (a) heating wood chips in a pre-cooker by means of water or steam, (b) then cooking the wood chips by means of steam in a cooker (14), and then (c) defibrating the wood chips in a refiner to produce fiber material, wherein (d) a portion of the steam is diverted after defibringing and used to heat or cook the wood chips.
[0003] According to a second aspect, the invention relates to a wood fiber production device for producing a wood fiber material, comprising (a) a pre-cooker for heating wood chips by means of water or steam, (b) a cooker, which is arranged downstream of the pre-cooker in the wood material flow direction (H), for cooking the wood chips by means of steam so that cooked wood chips are produced, (c) a refiner, which is arranged downstream of the cooker in the wood material flow direction (H), for defibrating the cooked wood chips so that fiber material is produced, (d) a steam branch, arranged downstream of the refiner in the wood material flow direction (H), for branching off part of the steam after defibringing, and (e) an exhaust steam line which connects the steam branch to the pre-cooker or cooker for supplying steam.
[0004] Wood fibers are made from wood and are used, for example, in the production of wood fiberboard or insulation material. The production of wood fiber requires large quantities of steam. WO 2015 / 014451 A1 describes a generic process in which steam is extracted from the fiber-steam stream using a cyclone downstream of the refiner. The partial diversion of steam downstream of the refiner and its use for heating or cooking the wood chips is also known from US Pat. No. 4,925,527. To prevent volatile organic substances contained in the wood from accumulating in the wood fiber, a portion of the steam is condensed, the terpene-rich components are separated, and the heat released during condensation is used to evaporate water. This process is complex and energy-inefficient. Therefore, there is a desire to reduce energy consumption.
[0005] CA 2346915 A1 discloses a process for purifying gases that are generated in the kraft process during pretreatment with black liquor, boiling in white liquor, washing and separation of pulp from black liquor, degradation of volatile organic components with superheated steam, delignification, washing and bleaching of the pulp, and combustion and regeneration of the black liquor, and are removed by ventilation. These gases are oxidized using air or ozone as an oxidizing agent at a maximum temperature of 100°C under heterogeneous catalysis. Such a process is not feasible with the steam that can be diverted after defibration due to its saturation with water vapor, as the water would condense at the low temperatures mentioned.
[0006] The invention is based on the object of reducing disadvantages in the prior art.
[0007] The invention solves the problem by a generic method comprising the step of introducing an oxidizing agent into the branched steam so that volatile organic substances contained in the steam are oxidized and purified steam is produced, wherein the purified steam is used at least partially for heating the wood chips.
[0008] The invention further solves the problem by means of a generic wood pulp production device which has a steam cleaner designed to introduce an oxidizing agent into the steam so that volatile organic substances contained in the steam are oxidized and purified steam is produced. The advantage of the invention is that it allows the production of wood pulp, for example in the production of wood fiber boards, such as LDF, MDF or HDF, with lower energy consumption. Because the diverted steam is purified, it can be used in the process without terpenes and / or aldehydes accumulating in the wood pulp. If the steam were not purified, volatile organic substances contained in the diverted steam, in particular terpenes and / or aldehydes, would settle on the wood chips and thus increase the concentration of these volatile organic substances in the wood pulp, which is undesirable.In addition, cleaning the steam generally prevents the volatile organic substances from settling on the exhaust steam line through which the diverted steam is led away from the steam branch.
[0009] In the context of the present description, a steam cleaner is understood to mean a device by means of which a VOC concentration (volatile organic compounds, volatile organic substances), in particular terpenes and / or aldehydes, can be reduced by at least 70% by chemical reaction of the volatile organic compounds with an oxidizing agent.
[0010] A wood fiber is understood, in particular, to mean a lignin-containing wood fiber. In particular, the process for producing the wood fiber is carried out as part of the production of a wood-based panel, wherein the wood fiber is used to produce the wood fiber panel.
[0011] Cooking wood chips specifically involves heating the wood chips with water and / or steam. The wood chips are first placed in the pre-cooker and then in the cooker.
[0012] Steam is a mixture of vaporous water and air, especially water vapor.
[0013] A wood fibre board is understood to mean in particular an LDF, MDF or HDF.
[0014] Instead of cooked wood chips, one could also speak of heated wood chips. The oxidizing agent is preferably a flameless oxidizing agent. According to one embodiment, the oxidizing agent contains oxygen. It is advantageous if the oxidizing agent releases elemental oxygen upon reaction with terpenes and / or aldehydes.
[0015] The oxidizing agent is preferably liquid. For example, the oxidizing agent is hydrogen peroxide. Alternatively, the oxidizing agent is ozone. When referring to hydrogen peroxide, this also includes an aqueous solution of hydrogen peroxide. The hydrogen peroxide may contain an Fe(II) salt, ammonium persulfate, cytochrome P450, monooxygenases, or ammonium peroxide. In particular, the oxidizing agent is not molecular oxygen or air.
[0016] It is advantageous that the diversion of steam, in particular the diverted steam mass flow, can be carried out independently of the type of wood chips used. In particular, it is advantageous that a material flow control of the diverted steam, as provided according to a preferred embodiment, can be independent of the type and / or properties of the wood chips used. This facilitates the control of the wood fiberboard production device. Instead, the oxidizing agent volume flow can be controlled to always keep the concentration of volatile organic substances below a predetermined maximum.
[0017] The feature that a portion of the steam is diverted after defibration is understood, in particular, to mean that steam is diverted from a steam-fiber stream leaving the refiner. In particular, the steam is diverted before the steam-fiber stream enters a blowline and / or a dryer.
[0018] According to a preferred embodiment, the wood chips are heated in the precooker using the purified steam. For this purpose, wood chips are brought into contact with the steam, for example, before cooking and shredding. According to one embodiment, the branched steam has a temperature above the boiling point of water at an introduction point where the oxidizing agent is introduced into the branched steam. In other words, the steam is free of water droplets. The oxidizing agent is thus introduced into a steam stream that may contain particles of terpenes and / or aldehydes. Because the steam stream contains no water droplets, the terpenes react particularly quickly and extensively.
[0019] According to one embodiment, a refiner outlet water concentration in mole percent of the steam at a refiner outlet differs by at most 0.9 times from an introduction point water concentration in mole percent that the branched steam has at an introduction point where the oxidant is introduced into the branched steam. In particular, no water is condensed out between the branching of the steam and the introduction of the oxidant.
[0020] According to one embodiment, the diverted steam is condensed essentially at the earliest, in particular only, during heating of the wood chips in the precooker. This feature is understood in particular to mean that at most 30 weight percent, in particular at most 20 weight percent, particularly preferably at most 10 weight percent, of the water contained in the diverted steam condenses before the steam is used to heat the wood chips in the precooker. The steam is preferably condensed during heating of the wood chips in the precooker.
[0021] It is advantageous to continuously measure the VOC concentration, i.e. the concentration of volatile organic substances, particularly terpenes and / or aldehydes, in the diverted steam. The VOC concentration is expressed, for example, as mass per steam volume or as a mass fraction of the steam. The VOC concentration is understood to be a concentration from which the concentration of volatile organic components can be determined. In particular, the TOC concentration of all organic carbon compounds is also a VOC concentration when it comes to compliance with an upper limit. Whenever VOC concentration is referred to below, the TOC concentration could also be generally referred to as TOC (total organic carbon).
[0022] Preferably, the introduction of the oxidant into the branched steam is controlled based on the VOC concentration. In other words, the amount of oxidant, namely the oxidant volume flow, introduced into the branched steam is increased as the VOC concentration increases. Additionally, the amount of oxidant introduced into the branched steam can be reduced as the VOC concentration decreases. In this way, on the one hand, sufficient oxidant is always introduced into the branched steam, and on the other hand, the consumption of oxidant is minimized. It is advantageous if this VOC concentration is measured in the direction of steam flow upstream of an introduction point at which the oxidant is introduced into the branched steam.
[0023] According to one embodiment, a second VOC concentration of volatile organic substances, in particular terpenes and / or aldehydes, is continuously measured in the diverted vapor. Preferably, the introduction of the oxidizing agent into the diverted vapor is also controlled or regulated based on the second VOC concentration.
[0024] If, for example, the second VOC concentration rises above a predetermined maximum concentration, according to a preferred embodiment, the amount of oxidant introduced per unit of time (oxidant flow) is increased. This occurs, in particular, even if the first VOC concentration remains unchanged.
[0025] If the second VOC concentration falls below a predetermined minimum concentration, the oxidant flow is reduced according to a preferred embodiment. This occurs especially even if the first VOC concentration remains unchanged.
[0026] Typically, a fiber material-steam mixture leaves the refiner. According to a preferred embodiment, no more than 40 mass percent of the steam in the fiber material-steam mixture is diverted. Diverting more steam usually complicates the conveying of the fiber material.
[0027] Alternatively or additionally, at least 10 percent by mass of the steam in the fiber material-steam mixture is diverted. This results in significant savings in the energy that would otherwise be required to generate the steam. The figures given are, for example, average values over 10 minutes.
[0028] According to one embodiment, the method comprises the step of irradiating the oxidizing agent with UV light. This results, for example, in the oxidizing agent forming radicals, in particular hydroxyl radicals. Preferably, the oxidizing agent is irradiated with UV light immediately before being introduced into the diverted vapor. In particular, the distance between the point at which the oxidizing agent is irradiated with UV light and the point at which the oxidizing agent first comes into contact with the diverted vapor is at most 10 m, in particular at most 5 m.
[0029] Preferably, the branched steam has a steam temperature of at least 100°C, especially at least 110°C, when the oxidant is introduced. At higher temperatures, the oxidant reacts more quickly with the volatile organic substances, so that lower concentrations of volatile organic substances can be achieved in the purified steam. It is advantageous if the steam temperature is no higher than 160°C. At even higher temperatures, the oxidant generally decomposes too quickly.
[0030] Preferably, the diverted steam has a pressure of at least 2 bar and / or at most 5 bar.
[0031] Preferably, the volatile organic substances react with the oxidant without catalyst. In other words, the diverted steam, into which the oxidant has been introduced, is not brought into contact with a solid catalyst. It has been found that a catalyst is unnecessary. Furthermore, a catalyst would reduce the flow velocity of the steam and thus reduce efficiency. Clogging of the catalyst, for example, with any fiber material contained in the diverted steam, is also avoided.
[0032] The method preferably comprises the step of applying glue, in particular using a blow line, to the wood fiber material and drying the glued fiber material. It is advantageous if the method includes the steps of spreading the, in particular dried, glued fiber material into a fiber cake and pressing the fiber cake to form the wood fiberboard. Pressing is carried out, for example, using a belt press.
[0033] In one embodiment, the steam cleaner comprises an introduction device for introducing the oxidizing agent into the steam line, by means of which diverted steam is discharged from the steam cleaner. For example, the introduction device is designed to inject or atomize the oxidizing agent.
[0034] The steam cleaner may have an oxidizing agent tank filled with oxidizing agent, for example, hydrogen peroxide. Preferably, the steam cleaner also has a pump for conveying the oxidizing agent to the introduction device. Alternatively or additionally, the steam cleaner may have an oxidizing agent generator by means of which the oxidizing agent can be produced. For example, the oxidizing agent generator may be an ozone generator. Alternatively or additionally, the steam cleaner may have an oxidizing agent container in which the oxidizing agent can be stored. For example, the oxidizing agent container is filled with hydrogen peroxide or ozone.
[0035] It is advantageous if the wood fiber board manufacturing device comprises a VOC concentration meter for measuring a (first) VOC concentration of volatile organic substances, in particular terpenes / or aldehydes, and / or the total concentration of organic carbon compounds in the steam in the steam flow direction upstream of an introduction point at which the oxidizing agent is introduced into the branched steam.
[0036] The dosing device is preferably designed to automatically introduce the oxidizing agent into the diverted steam based on the measured VOC concentration. In other words, the dosing device controls or regulates the oxidizing agent volume flow. For example, the dosing device contains a controllable pump and / or a controllable valve for this purpose.
[0037] The VOC concentration meter comprises, for example, a gas chromatograph with a flame ionization detector. The VOC concentration meter is preferably designed to automatically measure the VOC concentration at regular intervals, for example, more frequently than once per hour, in particular more frequently than once every half hour, and most preferably more frequently than once every 10 minutes.
[0038] Preferably, the wood pulp production device also comprises a flow meter for measuring a steam flow of diverted steam. The steam flow can be specified, for example, in mass per unit time or volume per unit time. It is advantageous if the steam branch is designed to divert a predetermined steam flow. For example, the steam branch has a valve that is controlled by a controller, the controller being connected to the flow meter. In this way, the valve is controlled in such a way that a predetermined target steam flow is always achieved.
[0039] In a preferred embodiment, the dosing device is designed to detect the VOC concentration from the VOC concentration meter and to automatically introduce the oxidizing agent into the diverted steam based on the VOC concentration and the steam flow. In other words, the volume flow of oxidizing agent introduced into the diverted steam per unit of time is calculated, in particular based on the VOC concentration and, if applicable, the steam flow, and the oxidizing agent is then introduced accordingly.
[0040] The wood pulp production device preferably has a first introduction device for introducing the oxidizing agent into the branched steam at a first introduction point.
[0041] It is particularly advantageous if the steam cleaner is designed to regulate the VOC concentration to a predefined VOC target concentration. If the measured VOC concentration deviates from the VOC target concentration, the oxidant flow rate is adjusted so that the measured VOC concentration approaches the VOC target concentration. If the measured VOC concentration is above the VOC target concentration, the oxidant flow rate is increased. If the measured VOC concentration is below the VOC target concentration, the oxidant flow rate is reduced.
[0042] According to a preferred embodiment, the wood pulp production device has a second VOC concentration meter for measuring a second VOC concentration (or a second TOC concentration) in the branched steam downstream of the introduction point in the steam flow direction. The feeder is designed to automatically introduce the oxidizing agent into the branched steam based on the first VOC concentration and the second VOC concentration, as well as, if appropriate, the steam flow. In other words, the feeder is designed to control or regulate the oxidizing agent volume flow based on the first and second VOC concentrations.
[0043] The wood pulp production device preferably has a second introduction device for introducing the oxidizing agent into the branched steam at a second introduction point located downstream of the first introduction point in the steam flow direction. The second introduction point is preferably located downstream of the second VOC concentration meter. It is advantageous if the steam cleaner is designed to control a second oxidizing agent volume flow rate, which is introduced at the second introduction point, depending on the second VOC concentration.
[0044] It is particularly advantageous if the steam cleaner is designed to regulate the second VOC concentration to a predetermined second VOC target concentration. If the measured second VOC concentration deviates from the second VOC target concentration, the first and / or second oxidant volume flow is adjusted so that the measured second VOC concentration approaches the second VOC target concentration. If the measured second VOC concentration is above the second VOC target concentration, the first and / or second oxidant volume flow is increased. If the measured second VOC concentration is below the second VOC target concentration, the first and / or second oxidant volume flow is reduced.
[0045] The wood pulp production device preferably has a bucket for applying glue to the fiber material. A bucket is understood to be a device by means of which the fiber material can be glued.
[0046] The wood fiber production device is preferably part of a wood fiberboard production device according to the invention for producing lightweight, medium-density fiberboards (LDF), medium-density fiberboards (MDF), and / or high-density fiberboards (HDF). The invention also relates to a wood fiberboard production device for producing a wood fiberboard, in particular an MDF board, comprising (a) a cooker for cooking wood chips using steam to produce cooked wood chips, (b) a refiner, arranged downstream of the cooker in the direction of wood material flow, for defibrating the cooked wood chips to produce fiber material, and optionally (c) a feeder, in particular a blow line, arranged downstream of the refiner in the direction of wood material flow, for applying glue to the fiber material to produce glued fiber material.In the direction of wood material flow behind the refiner and in front of the side bucket, in particular a blow line, a steam branch for branching off steam is arranged and the wood pulp production device has a steam cleaner which is designed to introduce an oxidizing agent into the steam so that volatile organic substances contained in the steam are oxidized and purified steam is produced.
[0047] A wood fiberboard is a board made from wood. The wood fiberboard preferably has a thickness between 2 mm and 60 mm. The density of the wood fiberboard is preferably between 600 kg per cubic meter and 1000 kg per cubic meter. The wood chips are preferably wood chips.
[0048] Gluing can be carried out, for example, using a blow line. A hopper is preferably arranged downstream of the steam branch in the direction of wood material flow. The invention is explained in more detail below with reference to the accompanying drawings.
[0049] This shows
[0050] Figure 1 is a flow diagram of a wood fiber production device according to the invention for carrying out a method according to the invention and
[0051] Figure 2 shows a flow diagram of a wood fiber board manufacturing device according to the invention for carrying out a method according to the invention according to a second embodiment.
[0052] Figure 1 shows a flow diagram of a wood fiber production device 10 according to the invention for producing wood fiber 11. The wood fiber production device 10 has a digester 14, which receives heated wood chips 18 from a pre-digester 16. The wood chips 18 were cleaned by a washing system 24 before being introduced into the pre-digester 16. A refiner 32 is arranged downstream of the digester 14 in the wood material flow direction H, by means of which the wood chips 18 coming from the digester 14 are defibrated. Together with steam 26, a steam-fiber material mixture 38 is thus produced.
[0053] By means of a steam branch 36, steam 26 is branched off from the steam-fiber material mixture 38 and fed into an exhaust steam line 69. A steam cleaner 52 is arranged in the exhaust steam line 69. The steam cleaner 52 functions as described below in connection with Figure 2.
[0054] The steam-fiber material mixture 38 can be fed to a secondary bucket 40, which is preferably designed as a blow line, but this is not necessary. The steam-fiber material mixture 38 is fed to a dryer 44, from which steam 26 and dried wood pulp 11 exit.
[0055] The wood fiber material 11 is used, for example, for the production of insulation material, medium-density fiberboard (MDF), lightweight medium-density fiberboard (LDF), high-density fiberboard (HDF), plant substrate for plant cultivation, such as potting soil, or packaging material. Figure 2 shows the flow diagram of a wood fiberboard production device 10 according to the invention for producing a wood fiberboard 12 in the form of an MDF board.
[0056] The precooker 16 is fed with wood chips 18, which are produced, for example, using a chipper 20 and then optionally washed in the washing system 24. Roundwood 22 can be used as the raw material, but other wood sources are also possible. In the precooker 16, the wood chips 14 are heated with hot water and / or steam 26'. The water or steam 26' can be generated using a boiler. The heated wood chips 18 flow from the precooker 16 into the cooker 14.
[0057] Downstream of the digester 14 in the wood material flow direction H, the resulting steam-wood chip mixture 30 enters the refiner 32, where the fiber material 34 is produced. Downstream of the refiner 32 in the wood material flow direction H is the steam branch 36, by means of which the steam 26 can be branched off. For example, 20 to 30 mass percent of the steam contained in the steam-fiber material mixture 38 is branched off.
[0058] The remaining steam-fiber material mixture 38 is fed to a blow line 40, where it is coated with glue. The resulting glued fiber material 42 is fed to a dryer 44, where it is dried. The dried fiber material 42 is then fed to a spreader 46, which spreads a fiber cake 48. The fiber cake 48 is pressed into the wood fiber board 12 by means of a press 50.
[0059] The steam cleaner 52, arranged downstream of the steam branch 36 in the steam flow direction D, introduces an oxidizing agent 56 into the branched steam 26 at an introduction point 54. In this case, the oxidizing agent is hydrogen peroxide.
[0060] The steam cleaner 52 comprises an oxidant source 58, which in this case comprises an oxidant container 58 and a metering device 60 in the form of an oxidant pump. Using a VOC concentration meter 62, the steam cleaner 52 measures a first VOC concentration cvoc.i of volatile organic components in the branched steam 26. Depending on the VOC concentration, an oxidant volume flow Qse of oxidant 56 is introduced, for example, by injection, into the branched steam 26 by means of an introduction device 57. The oxidant 56 reacts with volatile organic components in the branched steam.
[0061] The steam cleaner 52 can have a second VOC concentration meter 64, which is located downstream of the introduction point 54 in the steam flow direction D. The second VOC concentration meter measures a second VOC concentration cvoc,2. In this case, this is the TOC concentration of the total concentration of organic compounds. If the second VOC concentration cvoc,2 is above a predetermined maximum concentration CVOC,max, the oxidant volume flow Q56 is increased.
[0062] The steam cleaner 52 regulates the second VOC concentration cvoc,2 to a VOC target concentration cvoc.soii by increasing or decreasing the oxidant volume flow Q56.
[0063] Alternatively, it is possible for the steam cleaner 52 to have an introduction device, for example a nozzle 66, for introducing oxidizing agent at a second introduction point 54' downstream of the second VOC concentration meter 64 in the steam flow direction D. Alternatively, it is possible for the oxidizing agent volume flow Q56 to be increased if the second VOC concentration cvoc,2 is above the maximum concentration CVOC,max. It is possible, but not necessary, for the same oxidizing agent to be introduced at both introduction points 54, 54'. In particular, it is possible for two different oxidizing agents to be used.
[0064] By introducing the oxidizing agent, purified steam 68 is produced, which is fed to the pre-cooker 16 via an exhaust steam line 69.
[0065] The steam cleaner 52 can have a light source 74, by means of which the oxidizing agent 56 can be irradiated with UV light. In this way, hydroxyl radicals are formed, which particularly effectively destroy the volatile organic substances in the diverted steam 26. In the wood fiberboard manufacturing device 10 shown in Figure 2, for example, 2.5 ±0.5 l of steam per hour are diverted from the steam branch 36. Instead of diverting, one can also speak of discharging. A steam temperature T26 is, for example, 140°C ± 5°C. The first VOC concentration meter 62 measures a first VOC concentration of cvoc.i = 350 mg / cubic meter. The oxidizing agent volume flow is then set to Q56 = 125 liters / hour. The oxidizing agent 56 in this case is a 10 percent (by weight) hydrogen peroxide solution. The second VOC concentration meter 64 then measures a second VOC concentration of cvoc,2 = CTOC,2 = 30 mg / cubic meter.
[0066] This corresponds to a reduction of over 90%.
[0067] List of reference symbols
[0068] 10 wood fiber board manufacturing device 60 dosing devices
[0069] 11 Wood pulp 62 first VOC concentration measurement
[0070] 12 wood fiberboard ser
[0071] 14 Cooker 64 second VOC concentration
[0072] 16 pre-cooker knives
[0073] 18 (wood) chips 66 second feeding device, second nozzle
[0074] 20 Hacker 68 purified steam
[0075] 22 Roundwood 69 Exhaust steam pipe
[0076] 24 car wash
[0077] 26 steam 70 branch valves
[0078] 72 Capacitor
[0079] 30 steam wood chip 74 light source
[0080] mixture
[0081] 32 Refiner cvoc,i first VOC concentration
[0082] 34 Fiber material cvoc,2 second VOC concentration
[0083] 36 Steam branch CvOC,max Maximum concentration and
[0084] 38 Vapor-fiber material mixture volatile organic compounds (VOC)
[0085] 40 Blow-Line, Beieimer cvoc.soii VOC target concentration
[0086] 42 glued fiber material D steam flow direction
[0087] 44 Dryer H Wood flow direction
[0088] 46 Spreader QS6 Oxidant Volume Flow
[0089] 48 Fiber cake T26 Steam temperature
[0090] 50 press
[0091] 52 steam cleaners
[0092] 54 Placement point
[0093] 54' second insertion point
[0094] 56 Oxidizing agents
[0095] 57 Insertion device, first nozzle
[0096] 58 oxidizer container
Claims
Patent claims 1. A method for producing a wood pulp, comprising the steps (a) heating wood chips (18) in a pre-cooker (16) by means of water or steam (26), (b) then cooking the wood chips (18) by means of steam (26) in a cooker (14), (c) then defibrating the wood chips (18) in a refiner (32) to produce fibrous material (34), (d) wherein a portion of the steam is diverted after defibration and used to heat the wood chips (18) in the pre-cooker (16), characterized by the step (e) introducing an oxidizing agent (56) into the branched-off steam (26) so that volatile organic substances contained in the steam (26) are oxidized and purified steam (68) is produced, the purified steam (68) being used at least partially to heat the wood chips (18).
2. Method according to claim 1, characterized in that (a) the branched steam has a temperature above the boiling point of water at an introduction point at which the oxidizing agent (56) is introduced into the branched steam and / or (b) a refiner outlet water concentration in mole percent of the steam (26) at an outlet of the refiner (32) differs by at most 0.9 times from an introduction point water concentration in mole percent that the branched steam (26) has at an introduction point at which the oxidizing agent is introduced into the branched steam (26).
3. Method according to one of the preceding claims, characterized by the steps: (a) continuously measuring a VOC concentration (cvoc ) of volatile organic substances, in particular terpenes and / or aldehydes, in the branched off steam (26) and (b) controlling the introduction of the oxidizing agent (56) into the branched steam (26) based on the VOC concentration (cvoc ).
4. Method according to one of the preceding claims, characterized by the steps: (a) continuously measuring a second VOC concentration (cvoc,2) of volatile organic substances, in particular terpenes and / or aldehydes, in the branched-off steam (26) and (b) controlling the introduction of the oxidizing agent (56) into the branched steam (26) based on the second VOC concentration (cvoc,2).
5. Method according to one of the preceding claims, characterized in that (a) the refiner (32) releases a fiber material-steam mixture (38) and (b) at most 40 mass percent and / or at least 10 mass percent of the steam (26) in the fiber material-steam mixture (38) is branched off.
6. Method according to one of the preceding claims, characterized by the step Irradiating the oxidizing agent (56) with UV light so that the oxidizing agent (56) forms radicals.
7. Method according to one of the preceding claims, characterized in that the branched steam (26) during the introduction of the oxidizing agent (56) (a) has a steam temperature (T26) of at least 100°C, in particular at least 110°C, and / or at most 160°C and / or (b) has a pressure of at least 2 bar and / or at most 5 bar.
8. Process according to one of the preceding claims, characterized in that the volatile organic substances react uncatalyzed with the oxidizing agent.
9. Method according to one of the preceding claims, characterized by the steps (a) gluing the fiber material (34) in a bucket (40), in particular a blow line, so that glued fiber material (42) is produced, (a) scattering the glued fiber material (34) to form a fiber cake (48) and (b) Pressing the fiber cake (48) into the wood fiber board (12).
10. Method according to one of the preceding claims, characterized by the step: producing insulation material, plant substrate for plant cultivation, a medium-density fiberboard, a high-density fiberboard or packaging material from the fiber material. 11 . Wood pulp manufacturing device for producing a wood pulp, with (a) a pre-cooker (16) for heating wood chips (18) by means of water or steam (26), (b) a cooker (14) arranged downstream of the pre-cooker (16) in the wood material flow direction (H) for cooking the wood chips (18) by means of steam (26), (c) a refiner (32) arranged behind the cooker (14) in the wood material flow direction (H) for defibrating the wood chips (18) to produce fibrous material (34), (f) a steam branch (36) arranged downstream of the refiner in the wood material flow direction (H) for branching off a portion of the steam (26) after defibration and (d) an exhaust steam line (69) connecting the steam branch (36) to the pre-cooker (16) for supplying steam (26), characterized by (e) a steam cleaner (52) designed to introduce an oxidizing agent (56) into the steam (26) so that volatile organic substances contained in the steam (26) are oxidized and purified steam (68) is produced.
12. Wood fiber manufacturing device according to claim 11, characterized by (a) a VOC concentration meter (62) for measuring a VOC concentration (cvoc ) of volatile organic substances, in particular terpenes and / or aldehydes, in the branched steam (26) in the steam flow direction (D) upstream of an introduction point (54) at which the oxidizing agent (56) is introduced into the steam (26), and (b) a dosing device (60) designed to automatically introduce the oxidizing agent (56) into the branched steam (26) based on the VOC concentration (cvoc ).
13. Wood fiber production device according to one of claims 11 or 12, characterized by (a) a second VOC concentration meter (64) for measuring a second VOC concentration (cvoc,2) in the branched steam (26) in the steam flow direction (D) behind the introduction point (54), (b) wherein the feeder (60) is configured to automatically introduce the oxidizing agent (56) into the branched vapor (26) based on the first VOC concentration and the second VOC concentration.
14. Wood pulp manufacturing device according to one of claims 11 to 13, characterized by an introduction device (66) which is designed to introduce oxidizing agent (56) into the branched steam at a second introduction point (54') which is located in the steam flow direction (D) behind the point at which the second VOC concentration (cvoc.2) is measured.
15. Wood fiber board manufacturing device according to one of claims 11 to 14, characterized by (a) a bucket (40), in particular a blow line, arranged behind the refiner (32) in the wood material flow direction (H) for gluing the fiber material (34) so that glued fiber material is produced, (b) a dryer (44) arranged behind the auxiliary bucket (40) in the wood material flow direction (H) for drying the glued fibre material (34), (c) a spreader (46) for spreading dried fiber material (34) into a fiber cake (48) and (d) a press (50), in particular a belt press, for pressing the fiber cake (48) into the wood fiber board (12).