Method for producing wood fiber material and wood fiber material production equipment

Abstract

The invention relates to a method for producing a lignocellulosic material (32), comprising the following steps: providing a cellulosic material (30); combusting the fuel (24) in the furnace (16), producing an exhaust gas (27); drying the fibrous material (30) in a dryer (28) with the exhaust gas (27), resulting in dried fibrous material (32) and steam (34); the steam (34) is discharged into the atmosphere (44), a portion of the steam (34) is refluxed into the furnace (16), and any volatile organic compounds contained in the refluxed steam (34) are combusted by measuring the total concentration (cVOC) of volatile organic compounds in the steam (34) and changing the refluxed portion (R) of the refluxed steam (34) as a function of the total concentration (cVOC).

Description

Technical Field

[0001] This invention relates to a method for producing wood-based fiber materials, comprising the following steps: (a) preferably providing fiber materials and / or burning fuel in a furnace to generate exhaust gas; (b) using the exhaust gas to dry the fiber materials in a dryer to obtain dried fiber materials and steam; and (c) venting the steam into the atmosphere, preferably (e) recirculating a portion of the steam back into the furnace such that any volatile organic compounds contained in the recirculated steam are burned. The invention also relates to a method for producing wood-based material boards, which includes the method of producing wood-based fiber materials of this invention.

[0002] According to a second aspect, the present invention relates to a wood fiber material production apparatus for producing wood fiber materials, comprising: (a) a furnace for burning fuel to generate exhaust gas; (b) a refiner configured to break down wood chips into fibers to obtain fibrous materials; (c) a dryer arranged downstream of the refiner in the direction of wood material flow for drying the fibrous materials using the exhaust gas to generate steam; (d) an exhaust system for discharging the steam generated in the dryer during the drying of the fibrous materials into the atmosphere; and preferably (e) a diversion device connected to the dryer for returning a portion of the steam to the furnace. The invention also relates to a wood-based panel production apparatus, particularly designed for producing medium-density or high-density fiberboard, the wood-based panel production apparatus comprising the wood fiber material production apparatus according to the present invention. Background Technology

[0003] During the production of wood-based fiber materials, particularly in the case of cork as in a preferred embodiment, volatile organic compounds (VOCs), especially terpenes and aldehydes, are released during the drying of the fiber materials. Emissions of VOCs into the atmosphere must be limited to meet legal requirements.

[0004] Limiting volatile organic compound (VOC) emissions typically requires the use of energy and / or chemicals, which is undesirable. For example, one could try washing out VOCs with water. However, this is largely ineffective because terpenes are almost insoluble in water, meaning additional measures must be taken.

[0005] WO 2018 / 157945 A1 discloses a wood fiber material production apparatus according to the method described above and the wood fiber material production apparatus described above, wherein the drying steam from the dryer is reintroduced into the furnace via a cyclone separator and a heat exchanger to burn any volatile organic compounds contained in the drying steam.

[0006] US 2011 / 0056090 A1 describes a method in which the dry steam is also partially recycled back into the furnace. Furthermore, volatile organic compounds contained in the dry steam are removed by thermal oxidation before entering the ventilation riser. Summary of the Invention

[0007] The present invention aims to reduce the emission of volatile organic compounds.

[0008] The present invention solves this problem by means of the method having the features of claim 1. According to a second aspect, the present invention solves this problem by means of the wood fiber material production equipment described above having the features of claim 10.

[0009] The present invention also addresses this problem by a method described above, the method comprising the steps of: (a) measuring (i) the concentration of nitrogen oxides c in the steam, particularly downstream of the dryer in the material flow direction and / or before the steam is discharged into the atmosphere. NOx (ii) the concentration of nitrogen oxides in the exhaust gas, particularly in the exhaust gas downstream of the combustion chamber and upstream of the dryer in the material flow direction. NOx , and (b) based on nitrogen oxide concentration c NOx The reflux portion R of the reflux steam is changed. Preferably, the method includes the steps described in the characterizing portion of claim 1. The preferred embodiments described below also relate to this approach.

[0010] The present invention also addresses the aforementioned problem through a wood fiber material production apparatus comprising: (a) a nitrogen oxide sensor for measuring (i) the nitrogen oxide concentration in steam (34) downstream of the dryer in the material flow direction and / or before steam is discharged into the atmosphere, or (ii) the nitrogen oxide concentration in exhaust gas downstream of the combustion chamber and upstream of the dryer in the material flow direction, wherein a diversion device is configured to measure the nitrogen oxide concentration c NOx The reflux section R of the reflux steam is automatically changed. Preferably, the wood fiber production equipment includes a tool for measuring the total concentration c of volatile organic compounds. VOC A concentration meter, wherein the diversion device is configured to adjust the concentration based on the total concentration c. VOC The reflux section of the reflux steam is automatically changed. The preferred embodiment described below also relates to this solution.

[0011] The advantage of this invention is that it can reduce the amount of volatile organic compounds emitted into the atmosphere using relatively simple technical means.

[0012] Another advantage is that the reduction of emitted volatile organic compounds can be influenced by the recirculation portion of the recirculated steam. The recirculation portion is the weight percentage of steam flowing back into the furnace relative to the total steam leaving the dryer. Any disadvantages caused by recirculated steam can generally be limited to the necessary limits.

[0013] Another advantage may be that the reduction in volatile organic compounds (VOCs) achieved through recirculation into the furnace makes any subsequent process steps to purify the steam before venting it into the atmosphere less complex. For example, if, as specified in a preferred embodiment, VOCs are washed out of the steam in a gas scrubber, wastewater that must be purified is generated. The lower the VOC content in the steam, the less wastewater is generated, and the less work is required for purification.

[0014] Within the scope of this specification, wood-based material boards specifically refer to LDF (low-density fiberboard, low-density wood fiberboard, 170-250 kg / m³), MDF (medium-density fiberboard), or HDF (high-density fiberboard) or wood fiber insulation boards. In particular, wood-based material boards are wood fiberboards.

[0015] Combustion refers to oxidation that accompanies the formation of a flame. The total concentration of volatile organic compounds in steam can, in principle, be measured at any location. However, it is practical to measure it before the steam is released into the atmosphere, particularly before it enters the exhaust system. For example, measurements can be taken upstream of a diversion device or between the diversion device and the exhaust system.

[0016] According to a preferred embodiment, the method includes the steps of removing volatile organic compounds using spray washing and / or electrofiltration before venting steam into the atmosphere. Spray washing can also be referred to as quenching. In particular, electrofiltration (also referred to as electrofiltration) is wet electrofiltration. For example, it uses a wet electrofiltration filter that removes particles by electrostatic charging. These particles are flushed out continuously or intermittently. Its advantage is that it reduces the particles released into the atmosphere.

[0017] It is advantageous if the recirculated steam is fed into the furnace's burners, mixing chamber, and / or combustion chamber. In the combustion chamber, the fuel to be burned is mixed with air and / or steam. By feeding steam into the combustion chamber, the steam is heated to particularly high temperatures, thereby efficiently burning volatile organic compounds. Alternatively or additionally, the recirculated steam can be returned to the furnace as secondary air (Beiluft) (also known as supply air). Secondary air refers to air or steam that is not introduced into the combustion chamber along with the fuel. In particular, the secondary air is introduced into the combustion chamber spatially separately from the air that has been mixed with the fuel before being introduced into the combustion chamber.

[0018] Preferably, the recirculation portion of the steam returned to the furnace is at most 35% by weight, particularly at most 30% by weight. A larger recirculation portion could lead to the accumulation of water in the exhaust gas used for drying the fiber materials, which is undesirable. The recirculation portion is preferably at least 10% by weight. However, it is also possible that at certain times, particularly at most half the time, the recirculation portion is less than 10% by weight, particularly zero. In other words, if any steam is recirculated, the recirculation portion is preferably at least 10% by weight.

[0019] According to one embodiment, the method includes the step of measuring the total concentration of volatile organic compounds in the steam. Preferably, the total concentration is measured downstream of the dryer in the direction of material flow, particularly upstream of the diversion device.

[0020] Preferably, the method includes the step of adding a reflux portion when the total concentration exceeds a predetermined maximum concentration. By adding the reflux portion, the concentration of volatile organic compounds released into the atmosphere is reduced. This ensures that the concentration does not exceed a predetermined limit above the maximum concentration. This limit is, for example, a legally mandated limit.

[0021] Preferably, the method includes the step of reducing the reflux portion when the total concentration drops below a predetermined minimum concentration. This is advantageous when reflux causes disadvantages, such as reduced furnace and / or dryer efficiency.

[0022] In particular, the method preferably includes the step of adjusting the reflux section to make the total concentration approach the target concentration.

[0023] According to one embodiment, the method includes the steps of: measuring (i) the nitrogen oxide concentration of nitrogen oxides in steam, particularly downstream of the dryer in the material flow direction and / or upstream of a splitting device where the recirculated steam to the furnace is split from the exhaust steam to the atmosphere, and / or (ii) the nitrogen oxide concentration of nitrogen oxides in exhaust gas, particularly downstream of the furnace and upstream of the dryer in the material flow direction. Recirculating steam to the furnace generally results in a decrease in the temperature of the exhaust gas, thereby resulting in a lower nitrogen oxide concentration. If the nitrogen oxide concentration exceeds a predetermined maximum nitrogen oxide concentration, the recirculation portion is preferably increased. Nitrogen oxides in the exhaust gas can improve the oxidation of volatile organic compounds. Therefore, preferably, the method includes the step of reducing the recirculation portion when the nitrogen oxide concentration drops below a minimum nitrogen oxide concentration.

[0024] The method preferably includes the following steps: (a) heating the wood chips in a pre-cooker using water or steam, the required thermal and / or mechanical energy being provided, for example, by burning fuel. The method preferably includes the following step: (b) cooking the wood chips, particularly after heating, in a cooker using steam, the steam preferably being generated by burning fuel. Preferably, the method includes defiberizing the cooked wood chips in a pulper to obtain a fibrous material. The fibrous material is preferably glued to obtain a glued fibrous material, wherein the glued fibrous material is dried. The pre-cooker may also be a washer, part of a washer, or a unit separate from a washer.

[0025] Preferably, the method includes the step of dispersing the dried fibrous material to form a fiber cake, and preferably includes the step of pressing the fiber cake to form a wood-based material board.

[0026] Preferably, the inlet temperature of the exhaust gas entering the dryer is at least 300°C, particularly at least 350°C. This achieves high drying performance and partially oxidizes volatile organic compounds. Alternatively or additionally, the inlet temperature is at most 450°C, particularly at most 450°C. This prevents temperature damage to the fibrous materials.

[0027] According to one embodiment, the outlet temperature of the steam leaving the dryer is at least 50°C, particularly at least 50°C. This prevents water condensation. Preferably, the outlet temperature is at most 90°C, particularly at most 80°C. This allows for the highest possible efficiency during drying.

[0028] The wood fiber material production equipment according to the invention preferably includes a concentration meter for measuring the total concentration of volatile organic compounds in the steam. For measuring the total concentration, the concentration meter is preferably arranged downstream of the dryer in the material flow direction. Preferably, the diversion device is designed to measure the total concentration c. VOC The reflux portion of the reflux steam is automatically changed. Preferably, the diversion device is designed to perform this automatically: (i) when the total concentration c VOC,ist Exceeding the predetermined maximum concentration c VOC,max When increasing the reflux portion of the reflux steam, and / or (ii) when the total concentration c VOC,ist Reduced to the predetermined minimum concentration c VOC,soll The following reduces the reflux section. Alternatively or additionally, the diversion device is designed to automatically adjust the reflux section so that the total concentration c VOC,ist Approaching the target concentration c VOC,soll The shunt device preferably has a control unit, such as an electronic, electrical, or analog control unit.

[0029] According to a preferred embodiment, the method includes the step of introducing an oxidant into steam to oxidize volatile organic compounds contained in the steam, thereby obtaining purified steam. The term "exhaust gas" may be used in place of the term "steam." It is advantageous if the oxidant is introduced into steam that is not returned to the furnace and whose material flow does not pass through the furnace into the atmosphere.

[0030] According to a preferred embodiment, a portion of the steam diverted in the refiner after fiber separation is used to heat the wood chips in the pre-cooker. This reduces the energy required during production.

[0031] Preferably, the method includes the steps of: introducing an oxidant into the split steam to oxidize any volatile organic compounds contained in the steam, resulting in purified steam, wherein the purified steam is used at least partially for heating the wood chips. The oxidant is preferably a reagent for flameless oxidation. According to one embodiment, the oxidant contains oxygen (sauerstoffhaltig).

[0032] The wood fiber material production equipment preferably comprises: (a) a precooker for heating wood chips using water or steam; (b) a cooker arranged downstream of the precooker in the direction of wood material flow for cooking the wood chips using steam to obtain cooked wood chips; and (c) a refiner arranged downstream of the cooker in the direction of wood material flow for defiberizing the cooked wood chips to obtain fibrous material. Preferably, the wood fiber material production equipment comprises: (d) a steam diverter arranged downstream of the refiner in the direction of wood material flow for diverting a portion of the steam after defiberization; and (e) a steam discharge line connecting the steam diverter to the precooker or cooker for supplying steam. The wood fiber material production equipment preferably includes a steam purifier configured to introduce an oxidant into the steam to oxidize any volatile organic compounds contained in the steam, resulting in purified steam.

[0033] A steam purifier is a device that can reduce the concentration of VOCs (volatile organic compounds), especially terpenes and / or aldehydes, by at least 70% through a chemical reaction between volatile organic compounds and oxidants.

[0034] It is advantageous if the oxidizing agent releases elemental oxygen upon reaction with terpenes and / or aldehydes. For example, oxidizing agents are hydrogen peroxide or ozone. When hydrogen peroxide is mentioned, it also refers to an aqueous solution of hydrogen peroxide. Hydrogen peroxide can contain Fe(II) salts, ammonium persulfate, cytochrome P450, monooxygenase, or ammonium peroxide. Specifically, the oxidizing agent is not molecular oxygen or air.

[0035] Advantageously, steam, particularly a mass stream of steam, can be diverted regardless of the type of wood chips used. In particular, advantageously, the material flow controller for the diverted steam, according to a preferred embodiment, does not depend on the type or properties of the wood chips used. This makes the wood fiberboard production equipment easier to control. Conversely, the oxidant volume flow can be controlled to keep it consistently below a predetermined maximum concentration of volatile organic compounds.

[0036] According to a preferred embodiment, the method includes the step of irradiating the oxidant with ultraviolet light. This, for example, causes the oxidant to form free radicals, particularly hydroxyl radicals. Preferably, the irradiation of the oxidant with ultraviolet light occurs just before the introduction of the split steam. In particular, the distance between the location where the oxidant is irradiated with ultraviolet light and the location where the oxidant first comes into contact with the split steam is at most 10 m, particularly at most 5 m.

[0037] Preferably, when the oxidant is introduced, the diverted steam has a steam temperature of at least 110°C. The oxidant reacts more rapidly with volatile organic compounds at higher temperatures, allowing for a lower concentration of volatile organic compounds in the purified steam. A steam temperature of up to 160°C is advantageous. At higher temperatures, the oxidant typically decomposes too quickly. The diverted steam preferably has a pressure of at least 2 bar and / or up to 5 bar.

[0038] The more volatile organic compounds (VOCs) are decomposed by introducing the oxidant into the split steam, the lower the VOC concentration in the steam released into the atmosphere. According to a preferred embodiment, the reflux section is selected to be close to the maximum possible reflux section, particularly at least 0.8 times the maximum possible reflux section, especially preferably at least 0.85 times, and particularly at least 0.9 times. The maximum possible reflux section is one that satisfies the condition that a higher reflux section would impede the function of the dryer to the point that the predetermined degree of drying could no longer be achieved. This keeps the amount of oxidant used low.

[0039] According to a preferred embodiment, the method includes the step of introducing an oxidant into the steam before venting the steam into the atmosphere. Preferably, the oxidant is vented into the portion of the steam that is not fed into the furnace. This ensures compliance with predetermined limits for the content of volatile organic compounds in the steam entering the atmosphere.

[0040] Preferably, an oxidant is introduced into the steam or a diverted steam stream, causing the oxidant to oxidize the volatile organic compounds in a non-catalytic manner. Although it is possible and covered by the present invention for wood fiber material production equipment to include a catalyst arranged to catalyze the reaction of the oxidant with the volatile organic compounds, its effectiveness is reduced due to the solids content.

[0041] Wood-based material board production equipment is preferably designed to produce MDF or HDF. Attached Figure Description

[0042] The invention will now be explained in more detail with the aid of the accompanying drawings. The drawings show:

[0043] Figure 1 A flowchart of a wood fiber material production apparatus according to the present invention is shown, which constitutes part of a wood-based material board production apparatus and is configured to perform the method according to the present invention. Figure 2 A flowchart is shown of a wood fiber material production apparatus according to a second embodiment of the present invention, used to perform the method according to the present invention. Detailed Implementation

[0044] Figure 1 A wood fiber material production apparatus 10 is depicted, which forms part of a wood-based material board production apparatus 12 for producing wood fiberboard 14 in the form of wood-based material panels. The wood fiber material production apparatus 10 has a furnace 16, which includes a mixing chamber 18, a burner 20, and a combustion chamber 22. Fuel 24, for example in the form of wood, waste wood, gas, and / or oil, and air are fed into the burner 20. Exhaust gas 27 is generated during the combustion of fuel 24.

[0045] Exhaust gas 27 is fed into dryer 28, and the glued fibrous material 30' is also fed into dryer 28. Dryer 28 dries fibrous material 30, resulting in dried fibrous material 32 in the form of wood fiber material 32 and steam 34. Steam 34 is fed into exhaust system 36.

[0046] The exhaust system 36 may include a gas scrubber 38 and / or an electrostatic filter 40, particularly in the form of a wet electrostatic filter. Steam 34 is released into the atmosphere 44 through the exhaust system 36, particularly through a flue 42.

[0047] The return flow Q of steam 34 is obtained through the diversion device 46. R It can be returned to furnace 16, while the exhaust flow Q of exhaust system 36 A The diversion device 46 is arranged at a point downstream in the material flow direction M by means of a separator 47, which separates the dried fiber material 32 from the steam 34. Preferably, the diversion device 46 is arranged downstream of the separator at a distance of less than 50 m, particularly less than 30 m.

[0048] Traffic Q R Q A Measured in weight or mass per unit of time, such as Newtons or kilograms per minute. Reflux portion R=Q R / (Q) R +Q A It is regulated by control unit 48, which can be an adjustment unit.

[0049] VOC concentration meter 50 is positioned downstream of dryer 28 in the material flow direction M and connected to control unit 48 to measure the total concentration of volatile organic compounds c. VOC,ist As a function of time t, it provides the corresponding concentration c that changes with time. VOC,ist .

[0050] If the total concentration c VOC,is t exceeds the predetermined maximum concentration c VOC,max The control unit 48 automatically adds a recirculation section R. The maximum concentration is selected so that when emitted into the atmosphere 44 at emission point 51, it does not exceed a predetermined limit c for the total concentration of volatile organic compounds. Grenz For example, the limit value c Grenz = 200 mg / m³.

[0051] If the total concentration c VOC,ist Reduced to the predetermined minimum concentration c VOC,min The control unit 48 then automatically reduces the reflux section R. Specifically, the control unit 48 can be configured to adjust the reflux section R so that the total concentration approaches the target concentration. For example, the control unit 48 is a PI (proportional-integral) controller or a PID (proportional-integral-derivative) controller.

[0052] The wood fiber material production equipment may include a washer 52 for washing wood chips 54, which may be made from, for example, fresh wood 56 and / or recycled wood 58. The washer may also be configured as a pre-cooker or include a pre-cooker. A cooker 60 is preferably arranged downstream of the washer 52 in the material flow direction M, through which the wood chips 54 are cooked using steam. A pulper 62 for breaking down the wood chips 54 into fibers is arranged downstream of the cooker 60 in the material flow direction M, resulting in fibrous material 30. The fibrous material 30 is glued in a blowpipe 64.

[0053] The dried fibrous material 32 is then fed into a classifier 66, which removes fine particles. The residue is dispersed in a disperser 68 to form a fiber cake 70, which is then pressed in a press, particularly a hot press 72, to form wood fiberboard 14.

[0054] The exhaust gas 27 entering the dryer 28 has an inlet temperature T E For example, in T E = 120°C and T E = Between 214°C. The steam has an outlet temperature T. A For example, in T A = 60°C and T A = Between 85°C. Steam 34 leaves dryer 28 at a volumetric flow rate, for example Q = 400,000 to 800,000 m³ / h, for example 600,000 m³ / h.

[0055] Figure 2 A flowchart of a wood fiberboard production apparatus 10 according to the present invention for producing wood fiberboard 12 in the form of MDF boards is depicted. Optional components are depicted or outlined with dashed lines. The wood-based material board production apparatus may include a pre-cooker 53, which is arranged upstream of a cooker 60 and downstream of a washer 52 in the material flow direction H. Downstream of the cooker 60 in the material flow direction H, the resulting steam-wood chip mixture 30 enters a refiner 62, in which fibrous material is produced. An optional steam diversion device 136 is arranged downstream of the refiner 32 in the wood material flow direction H, through which steam 126 can be diverted. For example, 20 to 30% by mass of the steam contained in the steam-fibrous material mixture is diverted.

[0056] The remaining steam-fiber material mixture is fed into the injection line 64. A steam purifier 152, arranged downstream of the steam splitter 136 in the steam flow direction D, introduces an oxidant 156 into the split steam 126 at inlet point 154. In this example, the oxidant is hydrogen peroxide. The steam purifier 152 includes an oxidant source 158, which in this example includes an oxidant container and an oxidant pump in the form of a metering device 160. Using a VOC concentration meter 162, the steam purifier 152 measures the first VOC concentration c of the volatile organic components in the split steam 126. VOC,1 Based on the VOC concentration, an oxidant volumetric flow Q is introduced through device 157. 156 Oxidant 156 is introduced into the split steam 126 in the form of, for example, by injection. Oxidant 156 reacts with the volatile organic components in the split steam.

[0057] The steam purifier 152 may include a second VOC concentration meter 164, located downstream of the introduction point 154 in the steam flow direction D. The second VOC concentration meter measures a second VOC concentration c. VOC,2 In this example, this is the TOC concentration, which represents the total concentration of organic compounds. If the second VOC concentration c... VOC,2 Above a certain maximum concentration c VOC,max Then the volume flow of the oxidant Q 156 Increase. Steam purifier 152 increases or decreases the oxidant volume flow Q. 156 The second VOC concentration c VOC,2 Adjust to the target VOC concentration c VOC,soll .

[0058] Alternatively, the steam purifier 152 may include an inlet device, such as a nozzle 166, downstream of the second VOC concentration meter in the steam flow direction D, for introducing an oxidant at the second inlet point 154'. Alternatively, if the second VOC concentration c VOC,2 Higher than the maximum concentration c VOC,maxThis can increase the oxidant volume flow Q. 156 It is possible, but not necessary, to introduce the same oxidant at both introduction points 154 and 154'. In particular, two different oxidants can be used.

[0059] An oxidant is introduced to generate purified steam, which is fed into the pre-cooker 53 via exhaust steam line 169. The steam purifier 152 may include a light source 174 through which the oxidant 156 is irradiated with ultraviolet light. This results in the formation of hydroxyl radicals, which are particularly effective at destroying volatile organic compounds in the diverted steam 126.

[0060] Alternatively, the wood-based material production equipment 10 may include an exhaust purifier 252, which is preferably arranged downstream of the diversion device 46 in the material flow direction M. The exhaust purifier 252 may also be referred to as a steam purifier, and introduces an oxidant 256 into the steam 34 (also referred to as exhaust 245) at an inlet point 254. In this example, the oxidant is hydrogen peroxide (H₂O₂).

[0061] Exhaust purifier 252 includes an oxidant source 258, which in this example includes an oxidant container and an oxidant pump in the form of a meter 260. Using a VOC concentration meter 262, exhaust purifier 252 measures a first VOC concentration c of volatile organic components in exhaust gas 245. VOC,1 Based on the VOC concentration, an oxidant volumetric flow Q is introduced through device 257. 256 Oxidant 256 is introduced into exhaust gas 245 at point 254, for example, by injection. Oxidant 256 reacts with volatile organic components in exhaust gas 245.

[0062] The exhaust purifier 252 may include a second VOC concentration meter 264, located downstream of the inlet point 254 in the exhaust flow direction D. The second VOC concentration meter measures a second VOC concentration c. VOC,2 In this example, this is the TOC concentration, which represents the total concentration of organic compounds. If the second VOC concentration c... VOC,2 Above a certain maximum concentration c VOC,max Then the volume flow of the oxidant Q 256 Increase.

[0063] For example, the maximum concentration corresponds to the predetermined exhaust gas limit concentration c. VOC,BREV For example, this is stipulated by law. However, it is also possible that the maximum concentration is lower than the exhaust emission limit concentration cV. OC,BREV This ensures that the exhaust concentration does not exceed the emission limit limit c. VOC,BREV For example, c VOC,max = f cVOC,BREV Safety factor f [0.75, ...,1]. The smaller the safety factor, the lower the exhaust emission limit concentration c. VOC,BREV The lower the probability of being exceeded at any given moment, the higher the amount of oxidant used. Exhaust purifier 252 increases or decreases the oxidant volume flow Q. 256 The second VOC concentration c VOC,2 Adjust to the target VOC concentration c VOC,soll .

[0064] Alternatively, the exhaust gas purifier 252 may include an inlet device, such as a nozzle 266, downstream of the second VOC concentration meter in the exhaust flow direction D, for introducing an oxidant at the second inlet point 254.2. Alternatively, if the second VOC concentration c VOC,2 Higher than the maximum concentration c VOC,max This can increase the oxidant volume flow Q. 256 It is possible, but not necessary, to introduce the same oxidant at both introduction points 254 and 254.2. In particular, two different oxidants can be used.

[0065] The exhaust gas purifier 252 may also have only one VOC concentration meter 264, which is arranged downstream of the introduction point 254 in the steam flow direction D, wherein the oxidant is introduced into the exhaust gas 245 only at this single introduction point 254. The introduction of the oxidant produces purified exhaust gas, which is discharged into the atmosphere through the flue 42.

[0066] The exhaust gas purifier 252 may include a light source 274 through which an oxidant 256 is irradiated with ultraviolet light. This results in the formation of hydroxyl radicals, which are particularly effective at destroying volatile organic compounds. Exhaust temperature T 45 For example, 45°C 5°C. The first VOC concentration meter 262 measures the first VOC concentration c. VOC,1 = 200 mg / standard cubic meter, for example, then adjust the oxidant volume flow rate to Q. 256 = 50 liters / hour. In this case, oxidant 256 is a 5% (by weight) hydrogen peroxide solution. Then, the second VOC concentration meter 264 measures the second VOC concentration c. VOC,2 = c TOC,2 = 90 mg / standard cubic meter. A standard cubic meter is the volume of gas occupying 1 cubic meter under standard conditions of 1013 hPa and 23°C.

[0067] Regardless of other features of the embodiments described, the wood fiber material production equipment 10 and / or wood-based material board production equipment 12 may include a diversion device 46 and a steam purifier 152, or a diversion device 46 and an exhaust purifier 252, or only the diversion device 46, or the diversion device 46, the steam purifier 152, and the exhaust purifier 252. Preferably, the diversion device 46 is adjusted to comply with the VOC limit c in the exhaust gas 245 entering the atmosphere. Grenz And minimize the consumption of oxidants 158 and 258.

[0068] A nitrogen oxide concentration meter 74 is positioned downstream of the dryer 28 in the material flow direction M and connected to the control unit 48 to measure the total nitrogen oxide concentration c. NOx In particular, as a function of time t, it provides the corresponding time-varying nitrogen oxide concentration c. NOx,ist .

[0069] If the actual total nitrogen oxide concentration c NOx,ist Exceeding the predetermined maximum nitrogen oxide concentration c NOx,max The control unit 48 automatically adds the reflux section R. The maximum nitrogen oxide concentration c is selected. NOx,ma x, so that the nitrogen oxide concentration at emission point 51 does not exceed the predetermined limit c. NOx,grenz For example, the limit value c NOx, Grenz = 40 µg / m³.

[0070] If the actual concentration c NOx,ist Reduced to the predetermined minimum concentration c NOx,min The control unit 48 then automatically reduces the reflux section R. Specifically, the control unit 48 can be configured to adjust the reflux section R to bring the total concentration close to the target concentration. For example, the control unit 48 can be designed as a PI or PID controller.

[0071] List of reference numerals 10. Wood fiber material production equipment 12 Wood-based material board production equipment 14. Wood-based material boards, wood fiberboard 16 furnaces 18 Mixing Chamber 20 Burners 22 Combustion Chamber 24 Fuel 26 Air 27 Exhaust gas 28 Dryer 30 Fiber Materials 30' bonded fiber material 32. Wood fiber materials, dried fiber materials 34 Steam 36 Exhaust System 38 Gas Scrubber 40 Electrostatic Filter 42. Flue 44 Atmosphere 46 Diverter 47 Separator 48 Control Unit 50 VOC concentration meter 51 emission points 52 Washer 53 Pre-cooker 54 Wood Chips 56 Fresh Timber 58 Recycled Timber 60 Steamer 62 Pulping Machine 64. Spraying pipeline and adhesive application device 66 Grading Machine 68 Disperser 70 Fiber Biscuits 72 Press 74 Nitrogen oxide concentration meter 126 Steam 136 Steam Diversion Device 152 Steam Purifier 154 Introduction Point 156 Oxidizing Agent 157 Introduction device 158 Oxidant Source 160 Measuring Instrument 162 VOC Concentration Meter 164 Second VOC Concentration Meter 166 nozzle 169 Steam exhaust pipeline 174 Light Source 245 exhaust 252 Exhaust Gas Purifier 254 Introduction Point 256 Oxidizing Agent 257 Introduction device 258 Oxidant Source 260 Measuring Instrument 262 VOC Concentration Meter 264 Second VOC Concentration Meter 266 nozzle 274 Light Source c concentration cGrenz Limit c VOC Total concentration c VOC,ist Total concentration c VOC,max Maximum concentration c NOx Nitrogen oxide concentration M Material flow direction Q A Emission stream Q R Reflux R reflux section t time T A outlet temperature T E Inlet temperature.

Claims

1. A method for producing wood fiber material (32), comprising the following steps: (a) Provide fiber materials (30), (b) Burning fuel (24) in furnace (16) produces exhaust gas (27). (c) The fibrous material (30) is dried in a dryer (28) using the exhaust gas (27) to obtain dried fibrous material (32) and steam (34), and (d) Discharge the steam (34) into the atmosphere (44). (e) A portion of the steam (34) is returned to the furnace (16) such that any volatile organic compounds contained in the returned steam (34) are burned. Its characteristics include the following steps: (f) Measure the total concentration of volatile organic compounds (VOCs) in the steam (34). VOC ),as well as (g) Based on the total concentration (c) VOC ) Change the reflux portion (R) of the reflux steam (34).

2. The method according to claim 1, characterized in that: According to the total concentration (c) VOC The change in the reflux portion (R) of the reflux steam (34) is: (a) When the total concentration (c) VOC,ist Exceeding the predetermined maximum concentration (c VOC,max When adding reflux steam (34), the reflux portion (R) is increased, and / or (b) When the total concentration (c) VOC,ist ) reduced to the predetermined minimum concentration (c VOC,soll When the value is below ), reduce the reflux portion (R), and / or (c) Adjust the reflux section (R) so that the total concentration (c VOC,ist Approaching the target concentration (c) VOC,soll ).

3. The method according to any one of the preceding claims, characterized by the following steps: Before releasing the vapor (34) into the atmosphere (44), volatile organic compounds are removed by spray washing and / or electrofiltration.

4. The method according to any one of the preceding claims, characterized by the following steps: An oxidant is introduced into the steam (34) that is not returned to the furnace and whose material flow does not pass through the furnace but enters the atmosphere, thereby oxidizing any volatile organic compounds contained in the steam (34) to obtain purified steam.

5. The method according to any one of the preceding claims, characterized by the following steps: (a) Measure the nitrogen oxide concentration of nitrogen oxides in the steam (34) downstream of the dryer and / or upstream of the diversion device in the material flow direction, or measure the nitrogen oxide concentration of nitrogen oxides in the exhaust gas downstream of the furnace and upstream of the dryer in the material flow direction, and (b) When the nitrogen oxide concentration exceeds a predetermined maximum nitrogen oxide concentration, the reflux portion is increased, and / or when the nitrogen oxide concentration drops below a minimum nitrogen oxide concentration, the reflux portion is decreased.

6. The method according to any one of the preceding claims, characterized in that: The steam (34) is fed into the burner (20), mixing chamber (18) and / or combustion chamber (22) of the furnace (16).

7. The method according to any one of the preceding claims, characterized in that: The steam (34) is refluxed between 10% and 35% by weight, particularly 30% by weight.

8. The method according to any one of the preceding claims, characterized by the following steps: (a) Heat the wood chips with water or steam in a precooker (54). (b) The wood chips (54) are then steamed in a steam cooker (60). (c) The wood chips (54) are then de-fibrinated in a refiner (62) to obtain fibrous material (30). (d) The fiber material (30) is then glued together to obtain glued fiber material (30'), and the glued fiber material (30') is dried to obtain dried fiber material (32). (e) Dispersing the dried fibrous material (32) to produce fiber cake (70), and (f) Press the fiber cake (70) to form a wood-based material board (14).

9. The method according to any one of the preceding claims, characterized in that: (a) The inlet temperature (T) of the exhaust gas (27) entering the dryer (28) E The temperature shall be at least 300°C, particularly at least 350°C, and / or at most 480°C, particularly at most 450°C, and / or (b) The outlet temperature (T) of the steam (34) leaving the dryer (28) A The temperature shall be at least 50°C, particularly at least 55°C, and / or at most 80°C, particularly at most 75°C.

10. A wood fiber material production equipment (10) for producing wood fiber materials, comprising: (a) Furnace (16), which is used to burn fuel (24) and produce exhaust gas (27). (b) A pulper (62) designed to break down wood chips (54) into fibers to obtain fibrous material (30). (c) A dryer (28) is arranged downstream of the refiner (62) in the material flow direction (M) and is used to dry the fibrous material (30) using the exhaust gas (27) to generate steam (34). (d) An exhaust system (36) for discharging the steam (34) generated during the drying of the fibrous material (30) in the dryer (28) into the atmosphere, and (e) A diversion device (46), which is connected to the dryer (28) and is used to return a portion of the steam (34) to the furnace (16). Its features are: (f) Concentration meter (50), which is used to measure the total concentration of volatile organic compounds (c VOC ), (g) wherein the diversion device (46) is designed to adjust according to the total concentration (c) VOC Automatically change the reflux portion (R) of the reflux steam (34).

11. The wood fiber material production equipment (10) according to claim 10, characterized in that, The diversion device (46) is designed to operate automatically: (i) When the total concentration (c VOC,ist Exceeding the predetermined maximum concentration (c VOC,max When adding reflux steam (34), the reflux portion (R) is increased, and / or (ii) When the total concentration (c) VOC,ist ) reduced to the predetermined minimum concentration (c VOC,min When the value is below ), reduce the recirculation portion (R), or (iii) Adjust the reflux section (R) to achieve the desired total concentration (c VOC,ist Approaching the target concentration (c) VOC,soll ).

12. The wood fiber material production equipment (10) according to claim 10 or 11, characterized in that: (a) A nitrogen oxide sensor for measuring the nitrogen oxide concentration in steam (34) downstream of the dryer and / or upstream of the diversion device in the material flow direction, or for measuring the nitrogen oxide concentration in the exhaust gas downstream of the furnace and upstream of the dryer, and (b) The diversion device (46) is designed to operate automatically: (i) When the nitrogen oxide concentration exceeds a predetermined maximum nitrogen oxide concentration, increase the reflux portion, and / or (ii) When the nitrogen oxide concentration drops below the minimum nitrogen oxide concentration, reduce the reflux portion.

13. The wood fiber material production equipment (10) according to any one of claims 10 to 12, characterized in that: The exhaust system (36) includes: (a) Gas scrubber (38), and / or (b) Electrostatic filters (40), particularly wet electrostatic filters.

14. The wood fiber material production equipment (10) according to any one of claims 10 to 13, comprising: (a) A digester (60) for cooking wood chips (54) using steam, wherein a pulper (62) is arranged downstream of the digester (60) in the material flow direction. (b) A glue applicator (64) is arranged downstream of the dryer (28) in the direction of wood material flow (M) and is used to glue the dried fiber material (30) to obtain glued fiber material (30). (c) A disperser (68) for dispersing a fiber cake (70) composed of glued fibrous material (30), and (d) A press for pressing the fiber cake (70) to form a wood-based material board (14).

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