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  • 1.
    Fernando, Dinesh
    et al.
    Wood Ultrastructure Research Centre (WURC), Department of Forest Products/Wood Science, Swedish University of Agricultural Sciences, Uppsala.
    Muhic, Dino
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Daniel, Geoffrey
    Wood Ultrastructure Research Centre (WURC), Department of Forest Products/Wood Science, Swedish University of Agricultural Sciences, Uppsala.
    Fundamental understanding of pulp property development under different thermomechanical pulp refining conditions as observed by a new Simons' staining method and SEM observation of the ultrastructure of fibre surfaces2011In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, no 6, p. 777-786Article in journal (Refereed)
    Abstract [en]

    The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons' staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under differentprocess conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP. © 2011 by Walter de Gruyter Berlin Boston.

  • 2.
    Muhic, Dino
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Improved energy efficiency in double disc chip refining2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The electrical energy consumption in thermomechanical pulping (TMP) is very high, in the range of 2 – 3 MWh/adt depending on process solution and on the product quality specifications for the paper product. Both pulpwood and energy prices have increased rapidly for some time. Due to this, the main focus of the research and development is on ways to reduce the electrical energy consumption in wood chip refining. As a step towards a more energy and cost

    ‐ effective refining process, Holmen Paper AB has invested in a new mechanical pulping process at its Braviken mill. In this case the primary refining stage consists of high consistency (HC) double disc refiners ‐

    RGP68DD (machines with two counter rotating discs).

    Earlier studies on the refining conditions, such as intensity and temperature, have indicated that it should be possible to improve the energy efficiency in double disc refining while maintaining the functional pulp properties such as tensile index.

    The main goal of this project was to improve the energy efficiency in double disc chip refining with 150 kWh/adt to corresponding pulp properties as measured on pulp samples after refiner. In order to further improve the basic understanding of what happens to the wood fibre material when changing the process conditions, the morphological and ultrastructural changes of fibres were also studied. This part of the research work was performed in cooperation with the research program; Collaborative Research on the Ultrastructure of Wood Fibres (CRUW).

    This licentiate project is a part of a large development project where different techniques to improve the energy efficiency has been evaluated by means of mill scale trials at the Holmen Paper Braviken Mill. The high consistency double disc chip refining part of the project was financed by The Swedish Knowledge Foundation, Metso Paper and Holmen Paper, in cooperation with FSCN (Fiber Science & Communication Network) at Mid Sweden University.

    The trials were made on one of the TMP lines at the Holmen Paper Braviken mill with Norway spruce as raw material. The influence of increased specific 

     

     

    refining energy on pulp properties were studied at different refining temperatures, refining intensity, pulp consistency and production rate. Results from these trials were later validated by means of long term trials. Intensity models and simulations for intensity changes by new segment design were made by Juha‐

    Pekka Huhtanen from Tampere University of Technology, Finland.

    The results show that the specific energy consumption to same tensile index can be improved by means of increasing the refining pressure/temperature. The energy efficiency was improved by 80

     

     

    ‐150 kWh/adt depending on load and the inlet‐

    and housing pressure. The largest relative specific energy efficiency improvement was reached at low specific energy consumption levels.

    Similar fibre surface ultrastructure characteristics are gained by pulps with high pressure/temperature and low specific energy consumption compared to low pressure/temperature and high specific energy consumption pulps.

    High pressure/temperature and high specific energy consumption resulted in significantly increase in the delamination/internal fibrillation of pulp fibres. The surface ultrastructure of these fibres exhibited exposed S2 layer with long ribbontype fibrillation compared to pulps produced with lower temperature and lower specific energy consumption. When the refiner was operated at high pressure, the tensile index was preserved over the whole plate life. The specific light scattering coefficient increased with increasing pressure/temperature. A reason for this could be increased intensity caused by decreased plate gap. Increased intensity by means of refiner segment design changes resulted in large specific light scattering coefficient increase at similar tensile index, lower shives content, lower average fibre length and lower CSF at same specific energy consumption. The fresh steam consumption was reduced by the increased refiner ressure/temperature.

     

     

  • 3.
    Muhic, Dino
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Huhtanen, Juha-Pekka
    Sundström, Lars
    Sandberg, Christer
    Ullmar, Mats
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Energy efficiency in double disc chip refining. Influence of intensity by segment design2010In: Proceedings of the 7th InternationalFundamental Mechanical Pulp Research Seminar, Nanjing, China (2010), 2010, p. 103-111Conference paper (Refereed)
  • 4.
    Muhic, Dino
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Huhtanen, Juha-Pekka
    Tampere Univ Technol, Energy & Proc Engn Inst, FIN-33101 Tampere, Finland .
    Sundström, Lars
    Holmen Paper AB Braviken Paper Mill, SE-60188 Norrkoping, Sweden .
    Sandberg, Christer
    Holmen Paper AB Braviken Paper Mill, SE-60188 Norrkoping, Sweden .
    Ullmar, Mats
    Metso Paper, SE-85194 Sundsvall, Sweden .
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Vuorio, Petteri
    Metso Paper Oy, FI-37601 Valkeakoski, Finland .
    Energy efficiency in double disc refining. Influence of intensity by segment design2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 3, p. 224-231Article in journal (Refereed)
    Abstract [en]

    The goal with this work was to study the effect of segment design on electrical energy consumption and pulp quality in double disc TMP production. Mill scale trials were performed with refiner segments from Metso, which were designed based on the fluid dynamics theory. The calculated intensity for the different segments was related to the measured pulp quality. Refining with the high intensity segments (Turbine (TM)) produced pulp with similar tensile index and a significantly higher specific light scattering coefficient at certain specific energy consumption when compared with the reference segments. One drawback with the high intensity segments was the limited operating window due to fibre cutting. The trials showed that segment performance can be modelled, which facilitates the development of new segment designs.

  • 5. Muhic, Dino
    et al.
    Sundström, L
    Nilsson, L
    Sandberg, C
    Ullmar, M
    Backlund, U
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Influence of temperature on energy efficiency in double disc chip refining2009In: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009, 2009, p. 344-347Conference paper (Refereed)
    Abstract [en]

    As part of the investment project at Holmen Paper Braviken, the primary stage refining system of counter-rotating RGP68DD refiners (Metso) has been investigated. It is considered to be one of the most energy efficient refiners when comparing to e.g. tensile index. The aim with this work is to optimize the refining conditions for the RGP68DD in regard to refining temperature. Full-scale trials were made where SEC and temperature were successively increased at the same time. The SEC was mainly controlled with motor load and production rate. Feed- and housing- pressure were used to control temperature. The results show that stable specific energy consumption, and refining conditions regarding temperature, resulted in a pulp with increased quality.

     

     

  • 6.
    Muhic, Dino
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Sundström, Lars
    Holmen Paper AB Braviken Paper Mill, SE-60188 Norrkoping, Sweden.
    Sandberg, Christer
    Holmen Paper AB Braviken Paper Mill, SE-60188 Norrkoping, Sweden..
    Ullmar, Mats
    Metso Paper, SE-85194 Sundsvall, Sweden.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Influence of temperature on energy efficiency in double disc chip refining2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 4, p. 420-427Article in journal (Refereed)
    Abstract [en]

    In 2008 Holmen Paper Braviken invested in a new TMP-line. The primary stage refining system of pressurized counter-rotating double disc chip refiners in this TMP line has been investigated. The aim of this work was to improve the energy efficiency through optimization of the refining temperature.The specific refining energy was varied at different refining temperatures. Inlet and housing pressures were used to control temperature. There was no pressure difference between inlet and housing pressure.An increased inlet- and housing pressure (from 4.6 up to 7.1 bar(g)) and thereby refining temperature resulted in a reduction of the energy consumption to same tensile index by 80-150 kWh/adt. The largest energy reduction was attained at low refining energy levels. An increase in energy efficiency may be explained by a decrease in plate gap, probably caused by softer fibre pad and lower steam volume. At constant specific refining energy and elevated temperature, the tensile index and light scattering coefficients were higher, shives content and average fibre length were lower. These results are probably due to the increased intensity resulting from the plate gap reduction.Increased refining pressure proved to have a positive effect on energy efficiency and pulp quality in a long term trial, i.e. throughout a plate-life.

1 - 6 of 6
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