Heat Transfer and Energy Efficiency in Infrared Paper Dryers
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Heat Transfer and Energy Efficiency in Infrared Paper Dryers Magnus Pettersson Department of Chemical Engineering Lund University, Sweden 1999 Lund U niversity Akademisk avhandling for avlaggande av teknologie doktorsexamen vid Tekniska fakulteten vid Lunds universitet. Avhandlingen kommer att forsvaras pa engelska vid en offentlig disputation pa Kemicentrum, Solvegatan 39, Lund, horsal C, ffedagen den 10 december 1999 kl. 10.15. Fakultetsopponent ar Prof. Jamal Seyed-Yagoobi, Department of Mechanical Engineering, Texas A&M University, College Station, Texas,USA. ' BUTTON OF THIS DOCUMENT IS UNLk. FOREIGN SALES PROHIBITED ENERGY EFFICIENCY AND HEAT TRANSFER IN INFRARED PAPER DRYERS Copyright © 1999 Magnus Pettersson All rights reserved Printed in Sweden by KFS AB, Lund, 1999 DEPARTMENT OF CHEMICAL ENGINEERING 1 LUND UNIVERSITY P.O. BOX 124 SE-221 00 LUND, SWEDEN ISSN 1100-2778 ISRN LUTKDH/TKKA-1007/l-98/(1999) ISBN 91-628-3733-8 DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Although this may seem a paradox, all exact science is dominated by the idea of approximation Lord Betrand Russel Organisation Document name LUND UNIVERSITY DOCTORAL DISSERTATION Department of Chemical Engineering I Date of issue November, 1999 CODEN: LUTKDH/TKKA-1007/1-98/(1999) Author(s) Sponsoring organisation Magnus Pettersson Sydkraft AB, Svenskt Gastekniskt Center Title and subtitle Heat Transfer and Energy Efficiency in Infrared Paper Dryers Abstract Infrared (IR) dryers are widely used in the paper industry, mainly in the production of coated paper grades. The thesis deals with various aspects of heat transfer and energy use in infrared heaters and dryers as employed in the paper industry. Both gas-fired and electric IR dryers are considered and compared. The thesis also provides an introduction to infrared heaters and infrared drying, including a review of recent literature in the field. The transport of thermal radiation inside a paper sheet was investigated and different IR dryers were compared in terms of their ability to transfer energy to the internal parts of a paper sheet. Although there were evident differences in the absorption of radiation between gas-fired and electric IR dryers, the distinction was found to not be as important as has generally been believed. The main differences appeared to be due to the choice of a one- or a two-sided dryer solution, rather than the spectral distributions emitted by the dryers. A method for evaluating the radiation efficiency of IR heaters was proposed. An electric IR heater was evaluated in the laboratory. The radiation efficiency of the heater was shown to be strongly dependent on the power level. The maximum efficiency, found at high power level, was close to 60 %. A procedure for evaluation of the total energy transfer efficiency of an infrared paper dryer was proposed and used in the evaluation of an electric IR dryer operating in an industrial coating machine. The efficiency of the dryer was roughly 40 %. A model for an electric IR heater was developed. The model includes non-grey radiative heat transfer between the different parts of the heater, as well as conduction in reflector material and convective cooling of the surfaces. Using IR module voltage as the only input, model predictions of temperatures and heat flux were found to agree well with experimental data both at steady state and under transient conditions. The model was also extended to include features typical of an industrial IR dryer and was used to predict trends in IR dryer efficiency in relation to changes in power level and in paper grade. Key words infrared, IR, paper, radiation, heat transfer, dryer, drying, energy, efficiency, gas, electricity, modelling, experimental, coating Supplementary bibliographical information Language English ISSN and key title 1100-2778 ISBN 91-628-3733-8 Recipient’s note Number of pages 186 Price Security classification Distribution by (name and adress) Dept Chem Eng. 1, Lund University P.O.Box 124, SE-221 00 Lund, Sweden I, the undersigned, being the copyright owner of the abstract of the above-mentioned dissertation, hereby grant to all reference sources permission to publish and disseminate the abstract of the above-mentioned dissertation. Signature Date November 1.1999 Acknowledgements Several people have given me assistance, information and inspiration over the last four and a half years and I would like to thank them all. There are also a few persons whom I feel need some special attention. First of all, I would like to thank my supervisor Stig Stenstrom for his guidance throughout the years and for giving me the freedom to follow my own path. I also thank Prof. Roland Wimmerstedt for his sound advice and continuous support. Several persons connected with different suppliers of infrared dryers have provided input to the thesis in the form of information, questions and comments in correspondence, on the phone or in person. I would like to thank them all. Special thanks, however, are due to Klas-Goran Dahl at Ircon Drying Systems AB, previously with Itronic Sweden AB, for always taking the time to discuss details of the design and application of IR dryers and for providing experimental equipment I would also like to mention Andy Buhr and Leif Johansson with Infrarddsteknik AB, who were invaluable in the experimental evaluation at Klippans Finpappersbruk. Hard Peltoniemi with IRT Finland OY has also provided valuable comments on several matters. Thanks are due to Rune Eriksson, Sydkraft Forsaljning AB for fruitful discussions on the use and costs of energy in industry and for passing on several interesting papers. I have also had help with literature and several interesting discussions on IR technology with present and former staff of both DGC and SGC, especially Asger Myken, Kenneth J0rgensen, Ole Madsen, Jorgen Thunell and Owe Jonsson. I am grateful to several persons at the Department of Heat and Power Engineering. Prof. Bengt Sunden for letting me ‘sit in' and ask questions on his lectures on thermal radiation. Prof. Laszlo Fuchs, Xue-Song Bai and Jorgen Held for rewarding courses and discussions of turbulent flow, turbulence modelling and turbulent combustion. I think that these discussions have been the most intellectually stimulating part of my work, even though that part of my project did not make it to this thesis. Leif Stanley and Hans-Olof Jedlid have been very skilful in solving practical problems with my experimental equipment. Bengt Bengtsson provided very useful expertise in all problems related to data acquisition and measurements on electric quantities. I would like to thank Anders Gransfors, Mats Galbe, Anders Jaretun, Henrik Kempe and others who have always been there to answer all my computer questions. I would also like to thank all former and present colleagues at the Department of Chemical Engineering 1, especially those who have shared the office with me and all members of the drying group, for putting up with me and my eagerness to share my point of view on everything. I have also appreciated all open-minded discussions with the ‘lunch team’. Finally I thank Ase, my beloved wife, for all encouragement and support in everyday life. Sydkraft AB and SGC (Svenskt Gastekniskt Center) are gratefully acknowledged for providing financial support throughout the course of this work. Popularvetenskaplig sammanfattning av avhandlingen De fiesta svenskar bar nog upplevt bur skont det kan varma i solen en klar vinterdag, trots att termometem visar minusgrader. Eller bur kallt det kanns pa ryggen en sommarkvall fastan man sa sitter sa nara en eld att det nastan branns. Bada erfarenhetema beror pa varmestralning som kan varma oss utan att luften omkring oss ar varm. Varmestralningen Iran brasan nar bara den sida vi vander mot lagoma och kylan pa ryggen beror pa luftens verkliga temperatur. Varmestralning ar alltsa ett valbekant fenomen som manniskan anvant sig av p& olika sbtt lika lange som elden. Det ar emellertid forst pa senare ar som man konsekvent boijat utnyttja de speciella egenskaper som varmeoverforing med straining bar i industriprocesser. Denna avhandling handlar om varmeoverforing och energieffektivitet vid anvandning av varmestralare inom pappersindustrin. Varme transporteras pa tre olika salt; genom ledning, konvektion och straining. Vid ledning transporteras varme genom kollision mellan molekyler som ligger nara varandra. Ett vardagligt exempel ar nar man branner sig pa en spisplatta. Vid konvektion transporteras molekylema med rorelsen bos en gas eller en vatska vilket okar varme- transporten. En hartork eller en torktumlare utnyttjar just konvektion, att rorelse bos den varma luften okar varmeoverforingen jamfort med stillastaende luft. Bade ledning och konvektion kraver att varmen overfors mellan molekyler. Varme kan ocksa transporteras med elektromagnetisk straining som inte kraver nagot energibarande medium. Detta ar den varme man kanner i solen eller nar man halier handen en bit ovanfor en varm platta. Den elektromagnetiska straining som ar av betydelse vid varmeoverforing kallas ofta infrared (IR) straining och bar vaglangder som ar nagot langre an synligt rott ljus. Vid rumstemperatur Sr varmestralningen i regel obetydlig men blir belt dominerande vid hogre temperatur. Nar temperaturen stiger blir vaglangdema bos stralningen ocksa allt kortare och en del blir synligt ljus. Detta marker vi genom att foremal som blir riktigt varma bdqar lysa svagt rott, de