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CN-121986200-A - Method for producing lignocellulosic material and lignocellulosic material production apparatus

CN121986200ACN 121986200 ACN121986200 ACN 121986200ACN-121986200-A

Abstract

The invention relates to a method for producing lignocellulosic material (32), comprising the steps of providing fibrous material (30), combusting fuel (24) in a furnace (16) to produce an exhaust gas (27), drying the fibrous material (30) in a dryer (28) with the exhaust gas (27) to obtain dried fibrous material (32) and steam (34), discharging the steam (34) into the atmosphere (44), and refluxing a portion of the steam (34) to the furnace (16), by burning any volatile organic compounds contained in the refluxed steam (34), by measuring the total concentration (c VOC ) of volatile organic compounds in the steam (34) and changing the refluxed portion (R) of the refluxed steam (34) in accordance with said total concentration (c VOC ).

Inventors

  • J. Hofer
  • J. Hash
  • N. Calva
  • V. Schwert

Assignees

  • 瑞士克罗诺泰克股份公司

Dates

Publication Date
20260505
Application Date
20240926
Priority Date
20231010

Claims (14)

  1. 1. A method of producing lignocellulosic material (32), comprising the steps of: (a) Providing a fibrous material (30), (B) Combusting a fuel (24) in a furnace (16) to produce an exhaust gas (27), (C) Drying the fibrous material (30) in a dryer (28) using the exhaust gas (27) to obtain a dried fibrous material (32) and steam (34), and (D) Discharging said steam (34) into the atmosphere (44), (E) Refluxing a portion of the steam (34) into the furnace (16) such that any volatile organic compounds contained in the refluxed steam (34) are combusted, The method is characterized by comprising the following steps of: (f) Measuring the total concentration (c VOC ) of volatile organic compounds in the vapour (34), and (G) The reflux portion (R) of the reflux stream (34) is varied according to the total concentration (c VOC ).
  2. 2. The method according to claim 1, characterized in that: -changing the reflux portion (R) of the reflux stream (34) according to the total concentration (c VOC ) is: (a) When the total concentration (c VOC,ist ) exceeds the predetermined maximum concentration (c VOC,max ), the reflux portion (R) of the reflux stream (34) is increased, and/or (B) When the total concentration (c VOC,ist ) falls below a predetermined minimum concentration (c VOC,soll ), the reflux portion (R) is lowered, and/or (C) The reflux portion (R) is adjusted such that the total concentration (c VOC,ist ) approaches the target concentration (c VOC,soll ).
  3. 3. The method according to any of the preceding claims, characterized by the steps of: Volatile organic compounds are removed by spray scrubbing and/or electrofiltration prior to releasing the vapor (34) to the atmosphere (44).
  4. 4. The method according to any of the preceding claims, characterized by the steps of: An oxidant is introduced into the steam (34) which is not refluxed into the furnace and whose material flow is not passed through the furnace to the atmosphere, thereby oxidizing any volatile organic compounds contained in the steam (34) to obtain purified steam.
  5. 5. The method according to any of the preceding claims, characterized by the steps of: (a) Measuring the nitrogen oxide concentration of nitrogen oxides in the steam (34) downstream of the dryer and/or upstream of the dividing means in the material flow direction, or measuring 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) The return portion is increased when the nitrogen oxide concentration exceeds a predetermined maximum nitrogen oxide concentration and/or the return portion is decreased when the nitrogen oxide concentration falls below a minimum nitrogen oxide concentration.
  6. 6. The method according to any of the preceding claims, characterized in that the steam (34) is fed into a burner (20), a mixing chamber (18) and/or a combustion chamber (22) of the furnace (16).
  7. 7. The method according to any of the preceding claims, characterized in that between 10 and 35 wt.%, in particular 30 wt.%, of the steam (34) is refluxed.
  8. 8. The method according to any of the preceding claims, characterized by the steps of: (a) The chips (54) are heated with water or steam in a pre-digester, (B) The chips (54) are then steamed in a digester (60), (C) The chips (54) are then defibrated in a refiner (62) to obtain a fibrous material (30), (D) Subsequently gluing the fibrous material (30) to obtain a glued fibrous material (30 '), drying the glued fibrous material (30') to obtain a dried fibrous material (32), (E) Dispersing the dried fibrous material (32) to produce a fibrous cake (70), and (F) The fiber cake (70) is pressed to form a wood based material board (14).
  9. 9. The method according to any of the preceding claims, characterized in that: (a) The inlet temperature (T E ) of the exhaust gas (27) into the dryer (28) is at least 300 ℃, in particular at least 350 ℃, and/or at most 480 ℃, in particular at most 450 ℃, and/or (B) The outlet temperature (T A ) of the steam (34) leaving the dryer (28) is at least 50 ℃, in particular at least 55 ℃, and/or at most 80 ℃, in particular at most 75 ℃.
  10. 10. A lignocellulosic material production apparatus (10) for producing lignocellulosic material, having: (a) A furnace (16) for burning fuel (24) to produce exhaust gas (27), (B) A refiner (62) designed to defibrate the wood chips (54) to obtain a fibrous material (30), (C) A dryer (28) arranged downstream of the refiner (62) in the material flow direction (M) and for drying the fibrous material (30) with the exhaust gas (27) to produce steam (34), (D) An exhaust system (36) for exhausting into the atmosphere steam (34) generated when drying the fibrous material (30) in the dryer (28), and (E) -a dividing means (46) connected to said dryer (28) and adapted to reflux a portion of said steam (34) into said furnace (16), The method is characterized in that: (f) A concentration meter (50) for measuring the total concentration (c VOC ) of the volatile organic compounds, (G) Wherein the dividing means (46) are designed to automatically change the return portion (R) of the returned steam (34) as a function of the total concentration (c VOC ).
  11. 11. The lignocellulosic material production plant (10) according to claim 10, wherein the flow splitting device (46) is designed to automatically perform: (i) When the total concentration (c VOC,ist ) exceeds the predetermined maximum concentration (c VOC,max ), the reflux portion (R) of the reflux stream (34) is increased, and/or (Ii) When the total concentration (c VOC,ist ) falls below a predetermined minimum concentration (c VOC,min ), the reflux portion (R) is lowered, or (Iii) The reflux portion (R) is adjusted so that the total concentration (c VOC,ist ) approaches the target concentration (c VOC,soll ).
  12. 12. The lignocellulosic material production apparatus (10) according to claim 10 or 11, wherein: (a) A nitrogen oxide sensor for measuring the nitrogen oxide concentration of nitrogen oxides in the steam (34) downstream of the dryer and/or upstream of the flow dividing device in the material flow direction, or downstream of the furnace and upstream of the dryer, and (B) Wherein the shunt device (46) is designed to automatically perform: (i) Increasing the return portion when the nitrogen oxide concentration exceeds a predetermined maximum nitrogen oxide concentration, and/or (Ii) And when the nitrogen oxide concentration is reduced below a minimum nitrogen oxide concentration, reducing the reflux part.
  13. 13. The lignocellulosic material production apparatus (10) according to any one of claims 10 to 12, wherein the exhaust system (36) comprises: (a) A gas scrubber (38), and/or (B) An electric filter (40), in particular a wet electric filter.
  14. 14. The lignocellulosic material production apparatus (10) according to any one of claims 10 to 13, having: (a) A digester (60) for digesting wood chips (54) with steam, wherein the refiner (62) is arranged downstream of the digester (60) in the material flow direction, (B) A sizing device (64) arranged downstream of the dryer (28) in the direction of flow (M) of the wood material and for gluing the dried fibrous material (30), resulting in a glued fibrous material (30), (C) A disperser (68) for dispersing the fibrous cake (70) consisting of the glued fibrous material (30), and (D) A press for pressing the fibrous cake (70) to form a wood based material board (14).

Description

Method for producing lignocellulosic material and lignocellulosic material production apparatus Technical Field The present invention relates to a method for producing lignocellulosic material comprising the steps of (a) preferably providing fibrous material and/or combusting fuel in a furnace to produce an exhaust gas, (b) drying the fibrous material in a dryer with the exhaust gas to obtain dried fibrous material and steam, and (c) venting the steam to the atmosphere, preferably (e) refluxing a portion of the steam to the furnace such that any volatile organic compounds contained in the refluxed steam are combusted. The invention also relates to a method for producing a wood-based material board comprising the method for producing a lignocellulosic material according to the invention. According to a second aspect, the invention relates to a lignocellulosic material production plant for producing lignocellulosic material, having (a) a furnace for combusting fuel to produce exhaust gases, (b) a refiner (Refiner) configured to defibrate wood chips to obtain fibrous material, (c) a dryer arranged downstream of the refiner in the direction of flow of the lignocellulosic material for drying the fibrous material with the exhaust gases to produce steam, and (d) an exhaust system for exhausting the steam produced in the dryer when drying the fibrous material to the atmosphere, and preferably (e) a flow dividing device connected to the dryer for recirculating a portion of the steam to the furnace. The invention also relates to a wood-based material board production apparatus, which is specifically designed for producing medium-density or high-density fiberboard, comprising a wood-based material production apparatus according to the invention. Background Volatile organic compounds, in particular terpenes and aldehydes, are released during the production of lignocellulosic materials, in particular when produced from cork as in a preferred embodiment, during the drying of the fibrous materials. The emission of volatile organic compounds into the atmosphere must be limited to meet legal requirements. Limiting the emission of Volatile Organic Compounds (VOCs) generally requires the use of energy and/or chemicals, which is undesirable. For example, an attempt may be made to wash out volatile organic compounds with water. However, this is largely ineffective because terpenes are almost insoluble in water, meaning that additional measures must be taken. WO 2018/157945 A1 discloses a lignocellulosic material production plant according to the method described above and according to the above, wherein drying steam from a dryer is reintroduced into the oven through a cyclone and a heat exchanger, burning any volatile organic compounds contained in the drying steam. US 2011/0056090 A1 describes a method in which the drying steam is also partly returned to the oven. In addition, the volatile organic compounds contained in the drying vapor are removed by thermal oxidation prior to entering the vent stack. Disclosure of Invention The present invention aims to reduce emissions of volatile organic compounds. The invention solves this problem by a method having the features of claim 1. According to a second aspect, the present invention solves this problem by a lignocellulosic material production plant as described above having the features of claim 10. The invention also solves this problem by a method as described above, comprising the steps of (a) measuring the nitrogen oxide concentration c NOx of nitrogen oxides in (i) the steam, in particular downstream of the dryer in the material flow direction and/or in the steam before the steam is discharged to the atmosphere, and/or (ii) the nitrogen oxide concentration c NOx of nitrogen oxides in the exhaust gas, in particular in the exhaust gas downstream of the combustion chamber and upstream of the dryer in the material flow direction, and (b) varying the reflux portion R of the reflux steam as a function of the nitrogen oxide concentration c NOx. Preferably, the method comprises the steps of the characterising part of claim 1. The preferred embodiments described below also relate to this solution. The invention also solves the problem by means of a lignocellulosic material production plant comprising (a) a nitrogen oxide sensor for measuring (i) the nitrogen oxide concentration of nitrogen oxides in the steam (34) downstream of the dryer in the material flow direction and/or before the steam is discharged to the atmosphere, or (ii) the nitrogen oxide concentration of nitrogen oxides in the exhaust gas downstream of the combustion chamber and upstream of the dryer in the material flow direction, wherein the flow dividing means are configured to automatically change the return portion R of the return steam in dependence on the nitrogen oxide concentration c NOx. Preferably, the lignocellulosic production plant comprises a concentration meter for measuring the total concentration c VOC