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Properties of wood chips for thermomechanical pulp (TMP) production as a function of spout angle
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN)
Department for Chemical Engineering, NTNU, Trondheim, Norway.
2011 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, no 6, p. 805-809Article in journal (Refereed) Published
Abstract [en]

Spruce woodchipswere produced under well-controlled conditions in a laboratory woodchipper at spout angles of 30°, 40°, and 50° at a cutting rate of 20 m s-1 and with a nominalchip length of 25 mm. Thechips were then refined under thermomechanical pulp (TMP) conditions in a pilot refiner plant. The pulpproperties such as freeness, average fiber length, and shives content were determined and evaluated as a function of specific energy consumption. For a first stage refining and for a freeness value of 350 ml, a decrease in specific electrical energy consumption could be achieved by performing thewood chipping at a spout angle of 50° as compared to 30° which is the spout angle commonly used. A patent application regarding this method has been filed and is pending. It is realized that a freeness value is not directly indicative of any quality measure, such as, for example tensile index and light scattering coefficient but the obtained results can be interpreted to be promising. Further studies are needed regarding the impact of the modified chipping process.

Place, publisher, year, edition, pages
Walter de Gruyter, 2011. Vol. 65, no 6, p. 805-809
Keywords [en]
Chip damage, Energy efficiency, TMP, Wood chipping
National Category
Other Chemical Engineering Mechanical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-11916DOI: 10.1515/HF.2011.087ISI: 000297527600004Scopus ID: 2-s2.0-80053577151OAI: oai:DiVA.org:miun-11916DiVA, id: diva2:343916
Available from: 2010-08-16 Created: 2010-08-16 Last updated: 2017-12-12Bibliographically approved
In thesis
1. On the wood chipping process: a study on basic mechanisms in order to optimize chip properties for pulping
Open this publication in new window or tab >>On the wood chipping process: a study on basic mechanisms in order to optimize chip properties for pulping
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In both the chemical and mechanical pulping process, the logs are cut into wood chips by a disc chipper before fibre separation. To make the wood chipping process more efficient, one have to investigate in detail the coupling between process parameters and the quality of the chips. One objective of this thesis was to obtain an understanding of the fundamental mechanisms behind the creation of wood chips. Another objective with the thesis was to investigate whether it was possible to, in a way tailor the chipping process so as to reduce the energy consumption in a following mechanical refining process.

Both experimental and analytical/numerical approaches have been taken in this work. The first part of the experimental investigations, were performed with an in-house developed chipping device and a digital speckle photography equipment.

The results from the experimental investigation showed that the friction between the log and chipping tool is probably one crucial factor for the chip formation. Further more it was found that the indentation process is approximately self-similar, and that the stress field over the entire crack-plane is critical for chip creation.

The developed analytical model predicts the normal and shear strain distribution and to be more specific, the model can predict the compressive stresses parallel to the fibre direction for an assumed linear elastic and orthotropic material. The analytical distributions were found to be in reasonable agreement with the corresponding distributions obtained from a finite element analysis.

To be able to study the chipping process under realistic conditions, which for example means to use chipping rates representative for a real wood chipper, a laboratory chipper was developed. Details regarding the chipper and how to evaluate the force measurements are given together with an example of how the force on the cutting tool (the knife) varies with time during cutting.

To investigate the influence of a certain chipping process parameter, the chips were after production in the laboratory chipper, refined in a pilot refiner during conditions optimized for TMP (thermomechanical pulp) and CTMP (chemithermomechanical pulp) processes. It was concluded that the details concerning the chip process had a large impact on e.g. the energy consumption in both first stage and second stage refining. Results showing this are given in this thesis.

Abstract [sv]

För både kemisk och mekanisk pappersmassa så tillverkas flis av trädstockar med hjälp av en skivhugg innan fibrerna separeras. För att göra flisningsprocessen mer effektiv, måste kopplingen mellan processparametrar och fliskvalitet studeras. Ett mål med denna avhandling är att ge fundamental kunskap om mekanismerna bakom bildandet av träflis.

Både experimentella och analytiska/numeriska metoder har använts i detta arbete. De experimentella undersökningarna har gjorts med hjälp av egen utvecklad utrustning.

Resultaten från den experimentella undersökningen visar att friktionen mellan stammen och flisningsverktyget har betydelse vid flisning. Vidare observerades det att inträngnings processen är approximativt självlik (self similar) och att det är spänningsfältet över hela sprickplanet som är kritiskt för bildandet av en flis.

Den utvecklade analytiska modellen förutsäger normal- och skjuvspänningsfördelningen över sprickplanet och kan mer specifikt förutsäga den kompressiva belastning som verkar parallellt fiberriktningen i ett linjärt elastiskt och ortotropt material (trä). De analytiskt bestämda fördelningarna stämmer relativt väl överens med motsvarande fördelningar beräknad med finit element analys.

För att kunna studera flisningsprocessen under realistiska förhållanden, vilket bl.a. betyder att skärhastigheter som är representativa för en verklig process skall användas, så utvecklades inom ramen för avhandlingsarbetet, en laboratoriesflishugg. Detaljer rörande flishuggen samt hur uppmätta lastsignaler skall utvärderas ges tillsammans med ett exmpel på hur kraften på skärverktyget (kniven) varierar under ett skärförlopp.

Inverkan av en viss flisningsprocessparameter undersöktes genom att flis tillverkades i laboratorieflishuggen varefter de raffinerades i en pilotraffinör under förhållanden som var optimerade för TMP (termomekanisk massa) och CTMP (kemitermomekanisk massa) processerna. Det konstaterades att detaljer i flisningsprocessen hade stor inverkan på t.ex. energiåtgången i både första stegs – och andrastegsraffinering. Resultat som verifierar detta ges i avhandlingen.

 

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet, 2010. p. 36
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 83
Keywords
Wood chipping, Chip formation, Digital Speckle Photography, Friction, Fracture Processes, Analytical model, Laboratory Wood Chipper, Force Measurement, Vibration Synthesis, Energy Efficiency, Chip Damage, TMP, CTMP
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-11911 (URN)978-91-86073-72-5 (ISBN)
Public defence
2010-05-21, O102, Holmgatan 10, Sundsvall, 10:15 (Swedish)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Submitted.

Available from: 2010-08-16 Created: 2010-08-16 Last updated: 2015-11-04Bibliographically approved

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Hellström, LisbethGradin, PerEngstrand, Per

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