Method and plant for producing a fibrous web

Abstract

The present invention relates to a method and a corresponding plant for producing a fibrous web, in particular a paper web, paperboard web or tissue web. The formation of the fibrous web is defined online as a controlled variable and is held at a preselectable set-point level by way of an automatic formation control system.

1 . A method for producing a fibrous web comprising the steps of: 
 defining a formation of the fibrous web online as a controlled variable; and    holding said formation of the fibrous web at a preselectable set-point level using an automatic formation control system.    
   
   
       2 . The method according to  claim 1 , wherein said formation is defined directly.  
   
   
       3 . The method according to  claim 2 , wherein said formation is defined by at least one formation sensor.  
   
   
       4 . The method according to  claim 1 , wherein said formation is defined indirectly by at least one auxiliary variable.  
   
   
       5 . The method according to  claim 4 , wherein said at least one auxiliary variable for indirectly defining said formation comprises a water quantity in a bar section of a forming unit, said water quantity being measured.  
   
   
       6 . The method according to  claim 1 , wherein said formation is held at said preselectable set-point level by a corresponding change of at least one set-point variable.  
   
   
       7 . The method according to  claim 6 , further comprising changing accordingly at least a material density in order to hold said formation at said preselectable set-point level.  
   
   
       8 . The method according to  claim 6 , further comprising changing accordingly at least a retention in order to hold said formation at said preselectable set-point level.  
   
   
       9 . The method according to  claim 6 , further comprising changing accordingly at least an opening cross-section of an outlet gap of a headbox nozzle in order to hold said formation at said preselectable set-point level.  
   
   
       10 . The method according to  claim 6 , further comprising changing accordingly at least one vacua in a region of a forming unit in order to hold said formation at said preselectable set-point level.  
   
   
       11 . The method according to  claim 6 , further comprising changing accordingly at least one bar pressure in a region of a forming unit in order to hold said formation at said preselectable set-point level.  
   
   
       12 . The method according to  claim 6 , further comprising changing accordingly at least a wrap angle, through which the fibrous web is conveyed over a curved surface, in order to hold said formation at said preselectable set-point level.  
   
   
       13 . The method according to  claim 12 , wherein said curved surface comprises a forming roller.  
   
   
       14 . The method according to  claim 6 , further comprising changing accordingly at least a mesh tension, with which an outer lying dewatering mesh is conveyed over a curved path, in order to hold said formation at said preselectable set-point level.  
   
   
       15 . The method according to  claim 14 , wherein said curved path comprises a forming roller.  
   
   
       16 . The method according to  claim 6 , wherein said at least one set-point variable includes an actuating range, said actuating range of said at least one set-point variable is limited to a preselectable extent.  
   
   
       17 . The method according to  claim 16 , further comprising measuring a value of at least one auxiliary variable, wherein said actuating range is limited as a factor of a measured value of said at least one auxiliary variable.  
   
   
       18 . The method according to  claim 17 , wherein said at least one auxiliary variable which is measured comprises a dry content of the fibrous web downstream from a forming unit.  
   
   
       19 . The method according to  claim 17 , wherein said at least one auxiliary variable which is measured comprises a value representative of a web take-off.  
   
   
       20 . The method according to  claim 17 , wherein said at least one auxiliary variable which is measured comprises a value representative of a web take-off from a central roller.  
   
   
       21 . The method according to  claim 16 , further comprising triggering an alarm upon reaching at least one preselectable limit of said actuating range of said at least one set-point variable.  
   
   
       22 . The method according to  claim 1 , wherein said formation of the fibrous web is defined at an exit of a forming unit.  
   
   
       23 . The method according to  claim 1 , further comprising entering at least one formation value defined online into a controller for controlling said formation, wherein said formation is held at said preselectable set-point level by said controller through accordingly changing at least one set-point variable.  
   
   
       24 . The method according to  claim 23 , further comprising entering a value of at least one auxiliary variable into said controller in order to limit an actuating range of at least one set-point variable as a factor thereof.  
   
   
       25 . The method according to  claim 1 , further comprising providing at least one Proportional-Integral-Derivative controller.  
   
   
       26 . The method according to  claim 1 , further comprising providing at least one state controller.  
   
   
       27 . The method according to  claim 1 , further comprising providing at least one controller with at least one self-learning control algorithm.  
   
   
       28 . The method according to  claim 1 , further comprising at least one soft sensor at least one of to define said formation and to measure at least one auxiliary variable.  
   
   
       29 . An industrial plant for producing a fibrous web, said plant comprising an automatic formation control system for defining a formation of the fibrous web online as a controlled variable and holding said formation of the fibrous web at a preselectable set-point level.  
   
   
       30 . The industrial plant according to  claim 29 , further comprising a device for directly defining said formation.  
   
   
       31 . The industrial plant according to  claim 30 , wherein said device for directly defining said formation comprises at least one formation sensor.  
   
   
       32 . The industrial plant according to  claim 29 , further comprising a device for indirectly defining said formation by an auxiliary variable.  
   
   
       33 . The industrial plant according to  claim 32 , wherein said device for indirectly defining said formation is configured for measuring a water quantity in a bar section of a forming unit.  
   
   
       34 . The industrial plant according to  claim 29 , wherein said automatic formation control system is configured for accordingly changing at least one set-point variable in order to hold said formation at said preselectable set-point level.  
   
   
       35 . The industrial plant according to  claim 34 , wherein said automatic formation control system is configured for accordingly changing at least a material density in order to hold said formation at said preselectable set-point level.  
   
   
       36 . The industrial plant according to  claim 34 , wherein said automatic formation control system is configured for accordingly changing at least a retention in order to hold said formation at said preselectable set-point level.  
   
   
       37 . The industrial plant according to  claim 34 , further comprising a headbox nozzle including an outlet gap having an opening cross-section, wherein said automatic formation control system is configured for accordingly changing at least said opening cross-section of said outlet gap of said headbox nozzle in order to hold said formation at said preselectable set-point level.  
   
   
       38 . The industrial plant according to  claim 34 , further comprising a forming unit, wherein said automatic formation control system is configured for accordingly changing at least one vacua in a region of a forming unit in order to hold said formation at said preselectable set-point level.  
   
   
       39 . The industrial plant according to  claim 34 , further comprising a forming unit, wherein said automatic formation control system is configured for accordingly changing at least one bar pressure in a region of said forming unit in order to hold said formation at said preselectable set-point level.  
   
   
       40 . The industrial plant according to  claim 34 , further comprising a curved surface, wherein said automatic formation control system is configured for accordingly changing at least a wrap angle, through which the fibrous web is conveyed over said curved surface, in order to hold said formation at said preselectable set-point level.  
   
   
       41 . The industrial plant according to  claim 40 , wherein said curved surface comprises a forming roller.  
   
   
       42 . The industrial plant according to  claim 34 , further comprising an outer lying dewatering mesh which is conveyed over a curved path, wherein said automatic formation control system is configured for accordingly changing at least a mesh tension, with which said outer lying dewatering mesh is conveyed over said curved path, in order to hold said formation at said preselectable set-point level.  
   
   
       43 . The industrial plant according to  claim 42 , wherein said curved path comprises a forming roller.  
   
   
       44 . The industrial plant according to  claim 29 , wherein the plant includes at least one set-point variable having an actuating range, said actuating range of said at least one set-point variable being limitable to a preselectable extent.  
   
   
       45 . The industrial plant according to  claim 44 , further comprising a device configured for measuring a value of at least one auxiliary variable, wherein said actuating range is accordingly limitable as a factor of a measured value of said auxiliary variable.  
   
   
       46 . The industrial plant according to  claim 45 , further comprising a forming unit, wherein said device for measuring said value of said at least one auxiliary variable is configured for measuring a dry content of the fibrous web downstream from said forming unit.  
   
   
       47 . The industrial plant according to  claim 45 , wherein said device for measuring said value of said at least one auxiliary variable is configured for measuring a value representative of a web take-off.  
   
   
       48 . The industrial plant according to  claim 45 , further comprising a central roller, wherein said device for measuring said value of said at least one auxiliary variable is configured for measuring a value representative of a web take-off from said central roller.  
   
   
       49 . The industrial plant according to  claim 29 , further comprising a device for triggering an alarm upon reaching at least one preselectable limit of an actuating range of at least one set-point variable.  
   
   
       50 . The industrial plant according to  claim 29 , further comprising a forming unit including an exit, wherein said formation of the fibrous web can be defined at said exit of said forming unit.  
   
   
       51 . The industrial plant according to  claim 29 , further comprising a controller configured for controlling said formation, for entering into said controller at least one formation value defined online, and for accordingly changing at least one set-point variable in order to hold said formation at said preselectable level.  
   
   
       52 . The industrial plant according to  claim 51 , wherein said controller is configured for entering into said controller a value of at least one auxiliary variable in order to limit an actuating range of at least one set-point variable as a factor thereof.  
   
   
       53 . The industrial plant according to  claim 29 , further comprising at least one Proportional-Integral-Derivative controller.  
   
   
       54 . The industrial plant according to  claim 29 , further comprising at least one state controller.  
   
   
       55 . The industrial plant according to  claim 29 , further comprising at least one controller with at least one self-learning control algorithm.  
   
   
       56 . The industrial plant according to  claim 29 , further comprising at least one soft sensor at least one of for defining said formation and for measuring at least one auxiliary variable.