Method and apparatus for controlling the operation of stock preparation of a paper machine

Abstract

A method and an apparatus for controlling the operation of stock preparation of a paper machine for preparing machine stock from component stocks. The stock preparation includes a plurality of successive blending points, where the component stocks are blended with each other, a second raw material of the machine stock is added to the stock and/or the stock is diluted by blending dilution water with the stock. The flow and/or consistency of one or more stocks arriving at a blending point and/or the flow and consistency of the stock leaving a blending point and/or the concentration of the second raw material of the machine stock in the stock is adjusted in such a manner that the flow and/or consistency of the stock and/or the concentration of the second raw material of the machine stock in the stock follow target values determined for them.

1 . A method of controlling the operation of stock preparation of a paper machine, the stock preparation being configured to produce machine stock to be fed to the short circulation of the paper machine either from one or more component stocks by blending them with each other, and the stock preparation including a plurality of successive blending points where the component stocks are blended with each other, a second raw material of the machine stock is added to the stock and/or the stock is diluted by blending dilution water with the stock 
 the method comprising    determining the consistency of one or more stocks arriving at a blending point or the concentration of the second raw material of the machine stock in the stock arriving at a blending point and by determining the consistency of the stock leaving a blending point or the concentration of the second raw material of the machine stock in the stock leaving a blending point,    by determining the flow of one or more stocks arriving at the blending point and the flow of the stock OM 3 ) leaving the blending point    determining a consistency prediction for the consistency of one or more stocks arriving at the blending point or a concentration prediction of the second raw material of the machine stock in the stock arriving at the blending point,    determining a flow prediction for the flow of the stock leaving the blending point,    determining a consistency target for the consistency of one or more stocks arriving at the blending point or a target concentration of the second raw material of the machine stock in the stock arriving at the blending point and/or by determining a consistency target for the consistency of the stock leaving the blending point or the target concentration of the second raw material of the machine stock in the stock leaving the blending point,    determining a flow target for the flow of one or more stocks arriving at the blending point and/or a flow target for the flow of the stock leaving the blending point and    adjusting the flow and/or consistency of one or more stocks arriving at the blending point and/or the concentration of the second raw material of the machine stock in the stock arriving at the blending point based on the flow prediction of the stock leaving the blending point and/or the consistency prediction of one or more stocks arriving at the blending point and/or the concentration prediction of the second raw material of the machine stock in such a manner that the flow of one or more stocks arriving at the blending point follows the determined flow target and/or the consistency follows the determined consistency target and/or the concentration of the second raw material of the machine stock in the stock follows the determined target concentration and/or    adjusting the flow and consistency of the stock leaving the blending point and/or the concentration of the second raw material of the machine stock in the stock leaving the blending point based on the flow prediction of the stock leaving the blending point and/or the consistency prediction of one or more stocks arriving at the blending point and/or the concentration prediction of the second raw material of the machine stock in such a manner that the flow of the stock leaving the blending point follows the determined flow target and the consistency follows the determined consistency target and/or the concentration of the second raw material of the machine stock in the stock (KM, OM 1 , OM 2 , OM 3 ) follows the determined target concentration.    
     
     
         2 . A method as claimed in  claim 1 , wherein the second raw material of the machine stock is a filler, additive or chemical.  
     
     
         3 . A method as claimed in  claim 1 , comprising controlling the machine stock flow from a blending/machine chest of the stock preparation 
 by determining a machine stock flow control message based on the machine stock consistency prediction, the machine stock flow, a machine stock flow control set value and a machine stock fiber flow target value trajectory, and    by controlling the machine stock flow from the blending/machine chest based on said machine stock flow control message.    
     
     
         4 . A method as claimed in  claim 3 , comprising 
 determining the machine stock flow prediction based on the measured machine stock flow and the machine stock control message and controlling the dosing of the component stocks and/or the second raw material of the machine stock based on the machine stock flow prediction.    
     
     
         5 . A method as claimed in  claim 4 , comprising determining the component stock total flow target based on measured component stock flows, a blending/machine chest surface level trajectory and the machine stock flow prediction.  
     
     
         6 . A method as claimed in  claim 5 , comprising determining a consistency prediction for each component stock based on a component stock chest, output consistency prediction and the measured component stock consistency.  
     
     
         7 . A method as claimed in  claim 6 , comprising determining a flow target for each component stock based on the consistency prediction of each component stock and the component stock total flow target.  
     
     
         8 . A method as claimed in  claim 7 , comprising controlling the dosing of each component stock from the component stock chest by 
 determining a component stock flow control message based on the flow of the component stock from the component stock chest, a component stock flow control set value and the component stock flow target and controlling the dosing of the component stock from the component stock chest based on said component stock flow control message.    
     
     
         9 . A method as claimed in  claim 8 , comprising determining the flow prediction of the component stock flowing from the component stock chest based on the component stock flow control message and the measured component stock flow.  
     
     
         10 . A method as claimed in  claim 9 , comprising controlling the dosing of the component stock from a stock tower based on the component stock flow prediction.  
     
     
         11 . A method as claimed in  claim 9 , comprising controlling the dilution of the component stock flowing from the component stock chest with dilution water by determining a dilution water flow control message based on the component stock chest output consistency prediction, the component stock consistency target value trajectory, the measured dilution water flow, a dilution water flow control set value and the component stock flow prediction and 
 controlling the dilution water flow based on the determined dilution water flow control message.    
     
     
         12 . A method as claimed in  claim 11 , comprising determining a dilution water flow prediction based on the dilution water flow control message and the measured dilution water flow.  
     
     
         13 . A method as claimed in  claim 12 , comprising controlling the dosing of the component stock from the stock tower of the stock preparation based on the dilution water flow prediction.  
     
     
         14 . A method as claimed in  claim 13 , comprising controlling the dosing of the component stock from the stock tower by 
 by determining a control message for the component stock flowing from the stock tower to the component stock chest based on the flow of the component stock flowing from the stock tower, a component stock flow control set value, a flow prediction for the component stock leaving the component stock chest and the component stock chest surface level target value trajectory and    by controlling the dosing of the component stock from the stock tower based on the control message of the component stock flowing from the stock tower to the component stock chest.    
     
     
         15 . A method as claimed in  claim 14 , comprising determining the flow prediction for the component stock flowing from the stock tower to the component stock chest based on the control message of the component stock flowing from the stock tower and the measured flow of the component stock flowing from the stock tower.  
     
     
         16 . A method as claimed in  claim 15 , comprising controlling the dilution of the component stock flowing from the stock tower to the component stock chest with dilution water to be mixed with the component stock by 
 determining the dilution water flow control message based on a consistency prediction for the component stock flowing from the stock tower, a consistency target value trajectory for the component stock flowing from the stock tower, the measured dilution water flow, a dilution water flow control set value and the flow prediction for the component stock flowing from the stock tower and    by controlling the dilution water flow based on the determined dilution water flow control message.    
     
     
         17 . A method as claimed in  claim 1 , wherein the consistency of one or more stocks arriving at the blending point or leaving the blending point or the concentration of the second raw material of the machine stock in the stock is determined by measuring or indirectly by using a process model descriptive of the operation of the stock preparation or a part thereof.  
     
     
         18 . A method as claimed in  claim 1 , wherein the flow of one or more stocks arriving at the blending point or leaving the blending point is determined by measuring or indirectly by using a process model descriptive of the operation of the stock preparation or a part thereof.  
     
     
         19 . A method as claimed in  claim 1. , comprising a control message including several future control steps for the flow of the machine stock, a component stock or the second raw material of the machine stock, 
 a flow target value trajectory for the flow of the machine stock, a component stock or the second raw material of the machine stock, a blending/machine chest or component stock chest surface level target value trajectory    and/or a control message including several future control steps of the dilution water flow by using a model predictive control method comprising a process model descriptive of the stock preparation or a part thereof and optimization, so that the cost function associated with the optimization is minimized.    
     
     
         20 . A method as claimed in  claim 17 , wherein the process model is a dynamic process model.  
     
     
         21 . An apparatus for controlling the operation of stock preparation of a paper machine, the stock preparation being configured to produce machine stock to be fed to the short circulation of the paper machine either from one or more component stocks by blending them with each other, and the stock preparation including a plurality of successive blending points where the component stocks are blended with each other, a second raw material of the machine stock is added to the stock and/or the stock is diluted by blending dilution water with the stock, 
 in that the apparatus being configured    to determine the consistency of one or more stocks arriving at a blending point or the concentration of the second raw material of the machine stock in the stock arriving at a blending point and to determine the consistency of the stock leaving a blending point (DP 4 , DP 6 ) or the concentration of the second raw material of the machine stock in the stock leaving a blending point,    to determine the flow of one or more stocks arriving at the blending point and the flow of the stock leaving the blending point,    to determine a consistency prediction for the consistency of one or more stocks arriving at the blending point or a concentration prediction of the second raw material of the machine stock in the stock arriving at the blending point, to determine a flow prediction for the flow of the stock leaving the blending point,    to determine a consistency target for the consistency of one or more stocks arriving at the blending point or a target concentration of the second raw material of the machine stock in the stock arriving at the blending point and/or to determine a consistency target for the consistency of the stock leaving the blending point or a target concentration for the second raw material of the machine stock in the stock leaving the blending point,    to determine a flow target for the flow of one or more stocks arriving at the blending point and/or a flow target for the flow of the stock leaving the blending point and to adjust the flow and/or consistency of one or more stocks arriving at the blending point and/or the concentration of the second raw material of the machine stock in the stock arriving at the blending point based on the flow prediction of the stock leaving the blending point and/or the consistency prediction of one or more stocks arriving at the blending point and/or the concentration prediction of the second raw material of the machine stock in such a manner that the flow of one or more stocks arriving at the blending point follows the determined flow target and/or the consistency follows the determined consistency target and/or the concentration of the second raw material of the machine stock in the stock follows the determined target concentration and/or to adjust the flow and consistency of the stock leaving the blending point and/or the concentration of the second raw material of the machine stock in the stock leaving the blending point based on the flow prediction of the stock leaving the blending point and/or the consistency prediction of one or more stocks arriving at the blending point and/or the concentration prediction of the second raw material of the machine stock in such a manner that the flow of the stock leaving the blending point follows the determined flow target (KA 4 FFTr, and the consistency follows the determined consistency target and/or the concentration of the second raw material of the machine stock in the stock follows the determined target concentration.    
     
     
         22 . An apparatus as claimed in  claim 21 , wherein the second raw material of the machine stock is a filler, additive or chemical.  
     
     
         23 . An apparatus as claimed in  claim 21  or  22 , wherein the apparatus is configured to control the machine stock flow from the blending/machine chest of the stock preparation in such a manner that the apparatus is configured 
 to determine a machine stock flow control message based on the machine stock consistency prediction, the machine stock flow, a machine stock flow control set value and a machine stock fiber flow target value trajectory, and    to control the machine stock flow from the blending/machine chest based on said machine stock flow control message.    
     
     
         24 . An apparatus as claimed in  claim 23 , wherein the apparatus is configured 
 to determine the machine stock flow prediction based on the measured machine stock flow and the machine stock control message and to control the dosing of the component stocks and/or the second raw material of the machine stock based on the machine stock flow prediction.    
     
     
         25 . An apparatus as claimed in  claim 24 , wherein the apparatus is configured to determine the component stock total flow target based on measured component stock flows, a blending/machine chest surface level target value trajectory and the machine stock flow prediction.  
     
     
         26 . An apparatus as claimed in  claim 25 , wherein the apparatus is configured to determine a consistency prediction for each component stock based on a component stock chest output consistency prediction and the measured component stock consistency.  
     
     
         27 . An apparatus as claimed in  claim 26 , wherein the apparatus is configured to determine a flow target for each component stock based on the consistency prediction of each component stock and the component stock total flow target.  
     
     
         28 . An apparatus as claimed in  claim 27 , wherein the apparatus is configured to control the dosing of each component stock from the component stock chest 
 by determining a component stock flow control message based on the flow of the component stock from the component stock chest, a component stock flow control set value and the component stock flow target and    by controlling the dosing of the component stock from the component stock chest based on said component stock flow control message.    
     
     
         29 . An apparatus as claimed in  claim 28 , wherein the apparatus is configured to determine the flow prediction of the component stock flowing from the component stock chest based on the component stock flow control message and the measured component stock flow.  
     
     
         30 . An apparatus as claimed in  claim 29 , wherein the apparatus is configured to control the dosing of the component stock from a stock tower based on the component stock flow prediction.  
     
     
         31 . An apparatus as claimed in  claim 29 , wherein the apparatus is configured to control the dilution of the component stock flowing from the component stock chest with dilution water by determining a dilution water flow control message based on the component stock chest output consistency prediction, the component stock consistency target value trajectory, the measured dilution water flow, a dilution water flow control set value and the component stock flow prediction and 
 by controlling the dilution water flow based on the determined dilution water flow control message.    
     
     
         32 . An apparatus as claimed in  claim 31 , wherein the apparatus is configured to determine a dilution water flow prediction based on the dilution water flow control message and the measured dilution water flow.  
     
     
         33 . An apparatus as claimed in  claim 32 , wherein the apparatus is configured to control the dosing of the component stock from the stock tower of the stock preparation based on the dilution water flow prediction.  
     
     
         34 . An apparatus as claimed in  claim 33 , wherein the apparatus is configured to control the dosing of the component stock from the stock towers by 
 by determining a control message for the component stock flowing from the stock tower to the component stock chest based on the flow of the component stock flowing from the stock tower, a component stock flow control set value, a flow prediction for the component stock leaving the component stock chest and the component stock chest surface level target value trajectory and    by controlling the dosing of the component stock from the stock tower based on the control message of the component stock flowing from the stock tower to the component stock chest.    
     
     
         35 . An apparatus as claimed in  claim 34 , wherein the apparatus is configured to determine the flow prediction for the component stock flowing from the stock tower to the component stock chest based on the control message of the component stock flowing from the stock tower and the measured flow of the component stock flowing from the stock tower.  
     
     
         36 . An apparatus as claimed in  claim 35 , wherein the apparatus is configured to control the dilution of the component stock flowing from the stock tower to the component stock chest with dilution water to be mixed with the component stock by 
 by determining the dilution water flow control message based on a consistency prediction for the component stock flowing from the stock tower, a consistency target value trajectory for the component stock flowing from the stock tower, the measured dilution water flow, a dilution water flow control set value and the flow prediction for the component stock flowing from the stock tower and    by controlling the dilution water flow based on the determined dilution water flow control message.    
     
     
         37 . An apparatus as claimed in  claim 21 , wherein the apparatus is configured to determine the consistency of one or more stocks arriving at the blending point or leaving the blending point or the concentration of the second raw material of the machine stock in the stock by measuring or indirectly by using a process model descriptive of the operation of the stock preparation or a part thereof.  
     
     
         38 . An apparatus as claimed in  claim 21 , wherein the apparatus is configured to determine the flow of one or more stocks arriving at the blending point or leaving the blending point by measuring or indirectly by using a process model descriptive of the operation of the stock preparation or a part thereof.  
     
     
         39 . An apparatus as claimed in  claim 21 , wherein the apparatus is configured to determine a control message including several future control steps for the flow of the machine stock a component stock or the second raw material of the machine stock, 
 a flow target value trajectory for the flow of the machine stock, a component stock or the second raw material of the machine stock, a blending/machine chest or component stock chest surface level target value trajectory    and/or a control message including several future control steps of the dilution water flow by using a model predictive control method comprising a process model descriptive of the stock preparation or a part thereof and optimization, so that the cost function associated with the optimization is minimized.    
     
     
         40 . An apparatus as claimed in  claim 37 , wherein the process model is a dynamic process model.  
     
     
         41 . A method of controlling the operation of stock preparation of a paper machine, the stock preparation being configured to produce machine stock to be fed to the short circulation of the paper machine either from one or more component stocks by blending them with each other, and in which stock preparation a second raw material of the machine stock is added to the stock and/or the stock is diluted by blending dilution water with the stock 
 by the method comprising    determining flow data and a flow prediction for the machine stock, determining flow data and a flow prediction for one or more component stocks,    transferring the flow data and flow prediction of a component stock along the dosing line of the stock preparation backwards in such a manner that adjustments controlling the stock flows forward along the dosing line utilize predicted future flow changes,    determining consistency data and a consistency prediction of one or more component stocks and/or the concentration of the second raw material of the machine stock in the stock and a concentration prediction in the stock and    transferring the consistency data and consistency prediction of a component stock and/or the concentration of the second raw material of the machine stock in the stock and a concentration prediction in the stock forward along the dosing line in the stock preparation and adjusting the flow and consistency of the stock flowing forward in the dosing line of the stock preparation and/or the concentration of the second raw material of the machine stock in the stock in such a manner that the adjustments controlling the consistency of the stock or the concentration of the second raw material of the machine stock in the stock utilize the predicted future consistency changes or the changes in the concentration of the second raw material of the machine stock in the stock.    
     
     
         42 . A method as claimed in  claim 41 , wherein the second raw material of the machine stock is a filler, additive or chemical.