Method and a plant for producing and treating wood fibres

Abstract

The present invention relates to a plant and a method for producing and treating wood fibres in a plant comprising a fibre-producing part having a chip preheater ( 1 ) and a beater ( 2 ) for freeing fibre from wood chips. Such a plant and such a method are included as parts in a continuous production process of board and the object is to reduce the emission discharges of foremost VOC and formaldehyde, during different parts of the process as well as from the finished product. The method comprises feeding of wood chips (A) into an upper part of the chip preheater ( 1 ), discharge of wood chips in the bottom of the chip preheater to a screw conveyor ( 12 ) for further transportation into the beater ( 2 ), compression of the wood chips in a compression zone ( 15 ) in the screw conveyor, supply of steam (B) into the lower part of the chip preheater for washing fed chips in the counterflow direction, disposal ( 8 ) of flue gases in the form of released organic emissions, steam and air in the upper part of the chip preheater, as well as disposal of flue gases generated during the compression through an outlet ( 13 ) arranged in the compression zone. The plant has the corresponding parts.

1 . A method for producing and treating wood fibers in a plant comprising a fiber-producing part having a chip preheater having an upper part and a lower part and a beater for freeing fiber from wood chips, comprising: 
 feeding wood chips into said upper part of said chip preheater,    discharging wood chips in said lower part of said chip preheater to a screw conveyor for further transport to said beater,    compressing said wood chips in a compression zone in said screw conveyor, thereby generating flue gases therein,    supplying steam into said lower part of said chip preheater for washing said wood chips in the counterflow direction,    disposing flue gases in the form of released organic emissions, steam and air in said upper part of said chip preheater, and    disposing of said flue gases generated during said compressing through an outlet arranged in said compression zone.    
   
   
       2 . A method according to  claim 1 , wherein disposing of said flue gases generated during said compressing is achieved by conveying said flue gasses back to said upper part of said chip preheater whereby said flue gasses are disposed of together with other flue gases from said chip preheater.  
   
   
       3 . A method according to  claim 1  including conveying said flue gases to a destruction device for destruction thereof.  
   
   
       4 . A method according to  claim 1  including measuring the temperature of said flue gases disposed of from said upper part of said chip preheater, measuring and controlling the pressure of said steam entering said chip preheater, comparing said temperature and pressure values, and controlling the flow of said flue gases from said upper part of said chip preheater based on said comparison, whereby the steam losses from said chip preheater are controlled.  
   
   
       5 . A method according to  claim 1  including adding a catcher agent to said wood chips upon their transport to said beater.  
   
   
       6 . A method according to  claim 1 , including producing and treating said wood fibers in said beater and sending said wood fibers from said beater to a drier and then to a scrubber, and cooling air leaving said drier before it is treated in said scrubber.  
   
   
       7 . A method according to  claim 6 , including heat exchanging said air leaving said drier with air entering said drier so that the air conveyed to said drier is heated and the air conveyed to said scrubber is cooled.  
   
   
       8 . A method according to  claim 6  including separating water drops in said scrubber by means of a demister device arranged at the air outlet from said scrubber.  
   
   
       9 . Apparatus for producing and treating wood fibers, comprising a fiber-producing portion including a chip preheater having an upper part and a lower part and a beater for freeing fiber from wood chips, said chip preheater having a chip inlet in said upper part of said chip preheater, a chip outlet in the lower part of said chip preheater, a steam inlet in said lower part of said chip preheater and an outlet at the top of said chip preheater for generated flue gases in the form of released organic emissions, steam and air, whereby chips fed into said chip preheater through said chip inlet are washed in the counterflow direction by means of steam supplied through said steam inlet, a screw conveyor for conveying said chips from said chip outlet to said beater including a compression zone, and a flue gas outlet arranged in said compression zone for disposal of evaporated moisture generated upon the compression of said wood chips containing said flue gases.  
   
   
       10 . Apparatus according to  claim 9 , including a connection line arranged between said flue gas outlet in said compression zone and said upper part of said chip preheater.  
   
   
       11 . Apparatus according to  claim 9  including a destruction arrangement for destroying said generated flue gases.  
   
   
       12 . Apparatus according to  claim 9 , including a temperature control device for measuring the temperature of said flue gases disposed of from the top of said chip preheater, and a pressure control device for measuring and controlling the pressure of said steam entering said steam inlet, and means for controlling the flow of said flue gases from said top of said chip preheater by comparing said temperature and pressure values, whereby the steam losses in said chip preheater are controlled.  
   
   
       13 . Apparatus according to  claim 9 , including catcher agent addition means for addition of a catcher agent to said wood chips upon said feeding of said wood chips into said beater.  
   
   
       14 . Apparatus according to  claim 9 , including a drier for drying said wood fibers from said beater a scrubber located downstream of said drier, conduit means for conveying air leaving said drier into said scrubber, and a cooling device for cooling said air entering said scrubber from said drier.  
   
   
       15 . Apparatus according to  claim 14 , wherein said cooling device comprises a heat exchanger for heat exchange between said air entering said drier air leaving said drier into said scrubber, whereby said air entering said drier is heated and said air conveyed to said scrubber is cooled.  
   
   
       16 . Apparatus according to  claim 14  wherein said scrubber comprises water supply means to cool and absorb existing flue gases into a water phase.  
   
   
       17 . Apparatus according to  claim 14 , including water supply means arranged between said drier and said scrubber for supplying water to cool and absorb existing flue gases into said water phase.  
   
   
       18 . Apparatus according to  claim 16  including additive supply means for supplying additives for chemical treatment of said supplied water.  
   
   
       19 . Apparatus according to  claim 14 , wherein said scrubber comprises a device for the separation of water drops.