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Modeling and Control of the Paper Machine Drying Section Ola Slätteke Automatic Control Modeling and Control of the Paper Machine Drying Section Modeling and Control of the Paper Machine Drying Section Ola Slätteke Department of Automatic Control Lund University Lund, January 2006 To Kristin Department of Automatic Control Lund University Box 118 SE-221 00 LUND Sweden ISSN 0280í5316 ISRN LUTFD2/TFRT 1075 SE 2006 by Ola Slätteke All rights reserved Printed in Sweden by Media-Tryck Lund 2006 Abstract The topic of this thesis is modeling and control of the last part of the paper machine – the drying section Paper is dried by letting it pass through a series of steam heated cylinders and the evaporation is thus powered by the latent heat of vaporization of the steam The moisture in the paper is controlled by adjusting the set point of the steam pressure controllers There exist several commercial incentives to focus on the performance of the moisture control The time to perform a grade change is often limited by the moisture and shorter grade change time is directly correlated to economic profit Studies have shown that the drying section uses Ҁ of the total energy requirement in paper making Reduced variations in moisture gives opportunity for target shifts (changed set point) which reduces the amount of raw material and steam requirement It also creates opportunity for increased production rate The thesis is divided in two parts The first part deals with the control of the steam pressure inside the cylinders Both a black-box model and a physical model are given for the steam pressure process A tuning rule for both PI and PID control is derived and various other controller structures are investigated Many of the results are verified by experiments on paper machines at different paper mills The second part of the thesis treats the moisture controller The physical model from the first part is expanded with a model for the paper This gives a complete simulation model for the drying section that is implemented in the object-oriented modeling language Modelica Two new approaches to control the moisture by feedback are evaluated The first utilizes the air around the paper in combination with the drying cylinders to improve the controller performance The second uses only the last part of the drying section to control the moisture, while the first part is put at an appropriate level Finally, feedforward of a surface temperature signal is examined Acknowledgements There are a number of people who have contributed to this thesis First of all I would like to thank my advisors Björn Wittenmark, Tore Hägglund, and Krister Forsman Our regular meetings have been very constructive and fruitful, and this thesis would not have been possible without their outstanding support At the same time, I have been given a large amount of independence in my research which is something I have appreciated I would also like to acknowledge some of the people at ABB; Per Sandström, Jonas Warnqvist, Jonas Berggren, and Alf Isaksson It has been a great experience working with all of you There are many people I have come in contact with at different paper mills during my research I would particularly like to mention all of my old colleagues at Stora Enso Nymölla It has also been a pleasure getting acquainted with Stefan Snygg at Stora Enso Hylte, Stefan Ericsson and Lars Jonhed at AssiDomän Frövi I have had the opportunity to work with a few people at the Department of Chemical Engineering in Lund; Magnus Karlsson, Stig Stenström, Bernt Nilsson, and Erik Baggerud Magnus really deserves an extra salute for the work we have done together; I have learnt a lot from him Much of the work on physical modeling in the last chapter was carried out on account of a large amount of inspiration by Karl Johan Åström It all started as a minor discussion and ended up as a major piece of work Working at the Department of Automatic Control in Lund is an honor and it is a great atmosphere to operate in I would like to thank all my colleagues for the years we have had together I will miss you During the last year of my PhD-studies I had the privilege to work for a month at the Pulp and Paper Centre, University of British Columbia, Vancouver, under direction of Prof Guy Dumont This was an instructive and very interesting time for me Finally I would like to thank ABB and the Swedish Foundation for Strategic Research (SSF) within the project CPDC for the financial support of the project ... divided into three main parts, the wire section, the press section, and the drying section, see Figure 1.1 When the stock enters the head box in the wire section, it contains roughly % of fibers... the drying section affects a lot of the important physical properties of the final product, such as paper sheet elasticity, twist, and curl ~ 140 m Wire section 99 % Press section 80 % 50 % Drying. .. Modeling and Control of Paper Moisture in the Drying Section Enhanced Moisture Control Using the Air System 143 6.1 A literature review of drying section models 144 6.2 The model