| 1. |
- Ekbåge, Daniel
(författare)
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Process modelling based on data from an evaporation and a CTMP process : Analysis of energy efficiency and process variability
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The manufacture of pulp and paper is an energy intensive process configured of several unit processes that shape a network of flows of wood chips, chemical pulp, mechanical pulp, paperboard, steam and other important components. Improved energy efficiency supports sustainability of the process and the products. With the purpose of monitoring and controlling, information from multiple process and quality variables is continuously collected in the process data system. This data may be of time-varying nature and the variability might potentially span from seasonal to time-wise shorter variations and there are in some cases a need for predicting certain properties.By applying models based on process data there is a potential to increase the knowledge of the process characteristics, investigate the applicability of predictive models and identify optimization opportunities. Based on data from an evaporation and a CTMP plant, process models have been developed with the aim of improving the energy efficiency and studying process variability.
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| 2. |
- Lundström, Lisa
(författare)
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Polyelectrolyte multilayers of cationic and anionic starch and their use for improving the strength of papers made from mechanical pulps
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Graphic paper is experiencing severe competition from other materials and, most of all, from other media. This means there is a great need to improve paper quality while reducing raw material and production costs. Polyelectrolyte multilayer (PEM) treatment (i.e., consecutively adding cationic and anionic polyelectrolytes to the charged surface of wood fibres and fines, to form layers of these polyelectrolytes on the fibres/fines) has in recent years been found to offer great potential both to introduce new properties and to improve the mechanical properties of papers made of the treated fibres. The main objective of this thesis was to develop a strategy for the PEM treatment of cationic and anionic starch to improve the mechanical properties of paper made of thermomechanical pulp (TMP), since PEM treatment of fibres has displayed great potential to improve the mechanical properties of sheets made of chemical pulp. Mechanical pulp, however, has a large fine material content. Since the fine material is highly charged, polyelectrolyte consumption would be unacceptably high if the entire pulp were PEM treated, so we applied PEM treatment only to a fibre fraction of the pulps in most trials in the present work. The polyelectrolytes used for PEMs have so far mostly been well-defined, expensive ones unsuitable for use in standard paper grades; to develop a more economically realistic alternative, we used cationic and anionic starches. PEM formation on SiO2 surfaces from three differently charged cationic and anionic starches was first evaluated at three different salt levels using quartz crystal microbalance with dissipation (QCM-D) and stagnation point adsorption reflectometry (SPAR). The starch combinations displaying the highest potential for stable PEM formation at higher salt concentrations were then evaluated on an entire TMP pulp, as well as on a fraction of the pulp to reduce the amount of starch needed for PEM formation. The results indicate that it is possible to form PEMs from cationic and anionic starch on a SiO2 surface. The charge density, salt concentration, and combination of starches all influenced PEM formation. PEM formation on mechanical fibres produced large improvements in the mechanical properties of the sheets made of the treated fibres, and the tensile index, stretch-at-break, Z-strength, and Scott bond values all increased. Fractionating the pulp and PEM treating only a fraction of the pulp, the long fibre and middle fraction, produced large decreases in the amount of starch needed and large improvements in the mechanical properties of the sheets when no fine material was subsequently added. As untreated fine material was subsequently added, the improvement in mechanical properties decreased. PEM formation produced almost no reduction in formation and only a slight increase in sheet density.
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| 3. |
- Muhic, Dino
(författare)
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Improved energy efficiency in double disc chip refining
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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