Methods and systems for controlling paper quality by adjusting fiber filter parameters

Abstract

Disclosed is a system that adjusts the operational parameters of a fiber filter apparatus to keep measured properties indicative of paper quality, such as the paper's porosity, within desired value ranges. A feedback loop may be set up in which input properties are read, such as the paper's porosity and the pollution content of the filtrate leaving the fiber filter. These inputs go into a predictive model that determines how to adjust the fiber filter's operational parameters in order to move the measured paper quality properties into their desired value ranges while accommodating other constraints on the fiber filter's operation. The model looks at positive and negative correlations between the operational parameters and the measured inputs. Having processed the inputs and predicted an outcome, the predictive model directs controllers to change the operational parameters of the fiber filter. The input properties are again read, and the feedback loop is repeated.

We claim:  
     
         1 . A method for controlling a property indicative of a quality of paper by adjusting an operational parameter of a fiber filter apparatus, the method comprising: 
 measuring a value of the property indicative of a quality of paper;    predicting how adjusting the operational parameter of the fiber filter apparatus will affect the value of the property indicative of a quality of paper; and    adjusting, based on the predicting, the operational parameter of the fiber filter apparatus to bring or to keep the value of the property indicative of a quality of paper within a desired value range.    
     
     
         2 . The method of  claim 1  wherein the fiber filter apparatus recycles fibers received from a paper machine back to the paper machine.  
     
     
         3 . The method of  claim 1  wherein the fiber filter apparatus is part of a thermomechanical pulp system.  
     
     
         4 . The method of  claim 1  wherein the desired value range of the property indicative of a quality of paper is a single value.  
     
     
         5 . The method of  claim 1  wherein the property indicative of a quality of paper relates to a porosity of the paper.  
     
     
         6 . The method of  claim 1  wherein the operational parameter of the fiber filter apparatus relates to a rotation rate of a filter in the fiber filter apparatus.  
     
     
         7 . The method of  claim 1  wherein the operational parameter of the fiber filter apparatus relates to a ratio of sweetener added to an input to the fiber filter apparatus.  
     
     
         8 . The method of  claim 1  further comprising: 
 choosing a maximum adjustment rate for the operational parameter;  
 wherein the operational parameter is adjusted no faster than the maximum adjustment rate.  
 
     
     
         9 . The method of  claim 1  further comprising: 
 choosing a desired value range of a constraint property, the constraint property distinct from the property indicative of a quality of paper;  
 measuring the value of the constraint property;  
 predicting how adjusting the operational parameter of the fiber filter apparatus will affect the value of the constraint property; and  
 adjusting, based on the predicting, the operational parameter of the fiber filter apparatus to bring or to keep the value of the constraint property within the desired value range of the constraint property.  
 
     
     
         10 . The method of  claim 9  wherein the constraint property relates to a drop leg consistency and the desired value range of the constraint property is specified by a maximum desired consistency.  
     
     
         11 . The method of  claim 9  wherein the constraint property relates to a rotation rate of a filter in the fiber filter apparatus and the desired value range of the constraint property is a minimum desired rotation rate.  
     
     
         12 . The method of  claim 1  further comprising: 
 predicting how adjusting a second operational parameter of the fiber filter apparatus will affect the value of the property indicative of a quality of paper; and  
 adjusting, based on the predicting, the second operational parameter of the fiber filter apparatus to bring or to keep the value of the property indicative of a quality of paper within the desired value range.  
 
     
     
         13 . The method of  claim 1  further comprising: 
 measuring the value of an input property distinct from the property indicative of a quality of paper;  
 wherein the predicting is based in part on the value of the input property.  
 
     
     
         14 . The method of  claim 13  wherein the input property is in the set: motor load, chip moisture, temperature, pH level, flow rate.  
     
     
         15 . A computer-readable medium having instructions for performing a method for controlling a property indicative of a quality of paper by adjusting an operational parameter of a fiber filter apparatus, the method comprising: 
 measuring a value of the property indicative of a quality of paper;    predicting how adjusting the operational parameter of the fiber filter apparatus will affect the value of the property indicative of a quality of paper; and    adjusting, based on the predicting, the operational parameter of the fiber filter apparatus to bring or to keep the value of the property indicative of a quality of paper within a desired value range.    
     
     
         16 . A system for controlling a property indicative of a quality of paper, the system comprising: 
 a fiber filter apparatus;    a controller that adjusts an operational parameter of the fiber filter apparatus;    a sensor that measures the value of the property indicative of a quality of paper;    a computing device; and    a predictive control application running on the computing device that reads measurements produced by the sensor, predicts how adjusting the operational parameter of the fiber filter apparatus will affect the value of the property indicative of a quality of paper, and directs the controller to adjust the operational parameter of the fiber filter apparatus to bring or to keep the value of the property indicative of a quality of paper within a desired value range.    
     
     
         17 . The system of  claim 16  wherein the fiber filter apparatus recycles fibers received from a paper machine back to the paper machine.  
     
     
         18 . The system of  claim 16  wherein the fiber filter apparatus is part of a thermomechanical pulp system.  
     
     
         19 . The system of  claim 16  wherein the desired value range of the property indicative of a quality of paper is a single value.  
     
     
         20 . The system of  claim 16  wherein the property indicative of a quality of paper relates to a porosity of the paper.  
     
     
         21 . The system of  claim 16  wherein the operational parameter of the fiber filter apparatus relates to a rotation rate of a filter in the fiber filter apparatus.  
     
     
         22 . The system of  claim 16  wherein the operational parameter of the fiber filter apparatus relates to a ratio of sweetener added to an input to the fiber filter apparatus.  
     
     
         23 . The system of  claim 16  wherein the predictive control application directs the controller to adjust the operational parameter of the fiber filter apparatus no faster than a desired maximum adjustment rate.  
     
     
         24 . The system of  claim 16  further comprising: 
 a second sensor that measures the value of a constraint property, the constraint property distinct from the property indicative of a quality of paper;  
 wherein the predictive control application reads measurements produced by the second sensor, predicts how adjusting the operational parameter of the fiber filter apparatus will affect the value of the constraint property, and directs the controller to adjust the operational parameter of the fiber filter apparatus to bring or to keep the value of the constraint property within a desired value range.  
 
     
     
         25 . The system of  claim 24  wherein the constraint property relates to a drop leg consistency and the desired value range of the constraint property is specified by a maximum desired consistency.  
     
     
         26 . The system of  claim 24  wherein the constraint property relates to a rotation rate of a filter in the fiber filter apparatus and the desired value range of the constraint property is a minimum desired rotation rate.  
     
     
         27 . The system of  claim 16  further comprising: 
 a second controller that varies a second operational parameter of the fiber filter apparatus;  
 wherein the predictive control application predicts how adjusting the second operational parameter of the fiber filter apparatus will affect the value of the property indicative of a quality of paper and directs the second controller to adjust the second operational parameter of the fiber filter apparatus to bring or to keep the value of the property indicative of a quality of paper within a desired value range.  
 
     
     
         28 . The system of  claim 16  further comprising: 
 a second sensor that measures the value of an input property distinct from the property indicative of a quality of paper;  
 wherein the predictive control application reads measurements produced by the second sensor and bases its prediction in part on the value of the input property.  
 
     
     
         29 . The system of  claim 28  wherein the input property is in the set: motor load, chip moisture, temperature, pH level, flow rate.  
     
     
         30 . A computer-readable medium containing instructions for providing a system for controlling a property indicative of a quality of paper, the system comprising: 
 a fiber filter apparatus;    a controller that adjusts an operational parameter of the fiber filter apparatus;    a sensor that measures the value of the property indicative of a quality of paper;    a computing device; and    a predictive control application running on the computing device that reads measurements produced by the sensor, predicts how adjusting the operational parameter of the fiber filter apparatus will affect the value of the property indicative of a quality of paper, and directs the controller to adjust the operational parameter of the fiber filter apparatus to bring or to keep the value of the property indicative of a quality of paper within a desired value range.