Advanced

Static and Dynamic Modelling of the Drying Section of a Paper Machine

Karlsson, Magnus LU (2005)
Abstract (Swedish)
Popular Abstract in Swedish

Papperstillverkning inkluderar flera processteg såsom flisning av träråvaran, massakokning och avvattning med vakuumlådor, pressning och torkning. Flera modeller av de mest viktiga processerna i torkpartiet presenteras i denna avhandling. Modellerna beskriver både statiska och dynamiska förlopp. Nya reglerstrategier som kan användas för både reglering vid stationär drift och vid kvalitetsomställningar presenteras. De predikterade papperstemperaturerna verifierades med mätningar. Dessa mätningar bekräftade även de branta fuktprofiler som simuleringsprogrammet gav. Tillsammans med temperaturprofilen gav fuktprofilen en tryckprofil i pappersarket. Tryckprofilen visade att de kritiska partierna där... (More)
Popular Abstract in Swedish

Papperstillverkning inkluderar flera processteg såsom flisning av träråvaran, massakokning och avvattning med vakuumlådor, pressning och torkning. Flera modeller av de mest viktiga processerna i torkpartiet presenteras i denna avhandling. Modellerna beskriver både statiska och dynamiska förlopp. Nya reglerstrategier som kan användas för både reglering vid stationär drift och vid kvalitetsomställningar presenteras. De predikterade papperstemperaturerna verifierades med mätningar. Dessa mätningar bekräftade även de branta fuktprofiler som simuleringsprogrammet gav. Tillsammans med temperaturprofilen gav fuktprofilen en tryckprofil i pappersarket. Tryckprofilen visade att de kritiska partierna där papperet är svagt samtidigt som spänningarna är störst finns i den första tredjedelen av maskinen. I den sektionen är det mest troligt att papperet delaminerar. Beskrivningen om tryckgradienternas påverkan på delaminering stämde väl med data från ett verkligt delamineringsfall på bruket.



Vid stationär drift är det viktigt att upprätthålla en tillräckligt god papperskvalitet. Papperets fukthalt är en av kvalitetsparametrarna och denna regleras ofta med ångtrycken i cylindrarna. Störningar i torkpartiets inlopp sker med olika frekvens och reglersystemets uppgift är att återställa goda pappersegenskaper i utloppet så effektivt som möjligt vid sådana störningar.



Två reglersystem presenteras i denna avhandling. Den första baseras på mid-ranging och i den andra används framkoppling. Båda reglersystemen använder daggpunkten och påblåsningshastigheten i luftsystemet för att reglera högfrekventa störningar. Produktionsbortfallet vid kvalitetsomställningar kunde minskas med 60% med mid-ranging. Det framkopplade reglersystemet visade sig mycket effektivt vid fukthaltsstörningar. Mer arbete återstår för att på ett fördelaktigt sätt kunna integrera framkoppling även vid kvalitetsomställningar. (Less)
Abstract
The paper making process involves chopping of wood, cooking and forming, followed by dewatering in a vacuum section, press section and drying section. Several models for the most important parts of the paper machine drying section are presented in this thesis to describe phenomena at steady state and during state transitions. New control strategies applicable/useful for both steady-state control and for grade changes were derived. The predicted paper temperature was verified by surface measurements. These measurements also confirmed the steep moisture profile predicted by the model. The paper moisture and temperature profile determine the tension profile in the sheet. This profile showed that the critical section with respect to paper... (More)
The paper making process involves chopping of wood, cooking and forming, followed by dewatering in a vacuum section, press section and drying section. Several models for the most important parts of the paper machine drying section are presented in this thesis to describe phenomena at steady state and during state transitions. New control strategies applicable/useful for both steady-state control and for grade changes were derived. The predicted paper temperature was verified by surface measurements. These measurements also confirmed the steep moisture profile predicted by the model. The paper moisture and temperature profile determine the tension profile in the sheet. This profile showed that the critical section with respect to paper delamination is located in the first third of the machine. These predictions agreed well with machine data from a delamination case in the machine studied.



During steady-state operation it is important to maintain sufficiently good quality of the paper sheet. The moisture ratio is one property which is often controlled using the steam flow valve position. Disturbances at the inlet of the machine occur at various speeds due to upstream variations. During state transitions it is important to achieve an acceptable outlet moisture ratio as fast as possible.



Two control systems are presented in this thesis: one based on the mid-ranging technique and the other on a feedforward control system. Both control systems use the air dew point and the air impingement velocity to control rapidly occurring disturbances. The waste in production during a grade change could be reduced by 60% with the mid-ranging technique. The feedforward method showed potential in reducing the effect of moisture disturbances. More work is, however, needed to extend the use of the feedforward method to improve machine performance during grade changes. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Dumont, Guy, Professor at the department of Electrical and Computer Engineering, University of British Columbia,
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Pappers- och massateknik, Modelling, Wood, Paper, Multi-Cylinder, Simulation, Control, Steam, Air, Dew Point, Moisture Gradients, pulp and paper technology, Pressure Gradients
pages
166 pages
publisher
Department of Chemical Engineering, Lund University
defense location
Kemicentrum, hörsal B Getingevägen 60, Lunds Tekniska Högskola
defense date
2005-05-19 10:15
external identifiers
  • other:ISRN: LUTKDH/(TKKA-1002)/1-62/(2005)
ISSN
1100-2778
ISBN
91-628-6467
language
English
LU publication?
yes
id
70b00d67-d10d-4342-b465-f52624eb784e (old id 544618)
date added to LUP
2007-11-13 08:13:42
date last changed
2016-09-19 08:44:53
@phdthesis{70b00d67-d10d-4342-b465-f52624eb784e,
  abstract     = {The paper making process involves chopping of wood, cooking and forming, followed by dewatering in a vacuum section, press section and drying section. Several models for the most important parts of the paper machine drying section are presented in this thesis to describe phenomena at steady state and during state transitions. New control strategies applicable/useful for both steady-state control and for grade changes were derived. The predicted paper temperature was verified by surface measurements. These measurements also confirmed the steep moisture profile predicted by the model. The paper moisture and temperature profile determine the tension profile in the sheet. This profile showed that the critical section with respect to paper delamination is located in the first third of the machine. These predictions agreed well with machine data from a delamination case in the machine studied.<br/><br>
<br/><br>
During steady-state operation it is important to maintain sufficiently good quality of the paper sheet. The moisture ratio is one property which is often controlled using the steam flow valve position. Disturbances at the inlet of the machine occur at various speeds due to upstream variations. During state transitions it is important to achieve an acceptable outlet moisture ratio as fast as possible.<br/><br>
<br/><br>
Two control systems are presented in this thesis: one based on the mid-ranging technique and the other on a feedforward control system. Both control systems use the air dew point and the air impingement velocity to control rapidly occurring disturbances. The waste in production during a grade change could be reduced by 60% with the mid-ranging technique. The feedforward method showed potential in reducing the effect of moisture disturbances. More work is, however, needed to extend the use of the feedforward method to improve machine performance during grade changes.},
  author       = {Karlsson, Magnus},
  isbn         = {91-628-6467},
  issn         = {1100-2778},
  keyword      = {Pappers- och massateknik,Modelling,Wood,Paper,Multi-Cylinder,Simulation,Control,Steam,Air,Dew Point,Moisture Gradients,pulp and paper technology,Pressure Gradients},
  language     = {eng},
  pages        = {166},
  publisher    = {Department of Chemical Engineering, Lund University},
  school       = {Lund University},
  title        = {Static and Dynamic Modelling of the Drying Section of a Paper Machine},
  year         = {2005},
}