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  • 1.
    Berg, Jan-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Braviken Paper Mill, Holmen Paper, SE-60188 Norrkoping, Sweden.
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Low-consistency refining of mechanical pulp in the light of forces on fibres2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 2, p. 225-229Article in journal (Refereed)
    Abstract [en]

    The aim of this investigation was to find new approaches to evaluate the performance of low-consistency refiners. Data from a paper mill producing TMP from Norway spruce was used in order to find a possible way to calculate the power split between the zones in a TwinFlo refiner. An assumption of equal amount of fibres captured between overlapping bars was found successful in order to develop equations for the power split. The equations predicted equal power in both zones at equal disc gaps. The power was found to increase approximately linearly with decreasing disc gap over the range, 0.1-0.2 mm. The power split was essential to know for calculating refining intensities expressed as specific edge load and forces on fibres in the two zones. The reduction in fibre length was about 5% at 0.17 mm disc gap or at 0.03 N forces on fibres or at 0.7 J/m specific edge load. Disc gap, forces on fibres and specific edge load was found to predict fibre shortening approximately equally upon changes in power and flow rate through the refiner.

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  • 2.
    Berg, Jan-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper, Braviken Paper Mill, Sweden.
    Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    LC Refining Intensity In The Light Of Forces On Fibres2014In: International Mechanical Pulping Conference, IMPC 2014, Espoo: Paper Engineers' Association (PI) , 2014Conference paper (Refereed)
    Abstract [en]

    The aim of this investigation was to find new approaches to evaluate the performance of a full sized two-zoned low-consistency refiner i.e. a refiner with two stators and one rotor in between. Data from a paper mill producing TMP from Norway spruce was used in order to find a possible way to calculate the power split between the two zones. An assumption of equal amount of fibres captured between overlapping bars was found successful in order to develop equations for the power split. The equations predicted equal power in both zones at equal disc gaps. The power was found to correlate approximately linearly with the disc gap. The power split was essential to know for calculating refining intensity expressed as specific edge load and forces on fibres in the two zones. The reduction in fibre length was about 5% at 0.17 mm disc gap corresponding to 0.03 N force on fibres and 0.7 J/m specific edge load. Disc gap, force on fibres and specific edge load was found to predict the fibre shortening with approximately equal sufficiency upon changes in power and flow rate through the refiner.

  • 3.
    Ferritsius, Rita
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Stora Enso Kvarnsveden Mill, Borlänge, Sweden .
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper, Norrköping, Sweden .
    Ferritsius, Olof
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    LC-refining of mechanical pulps and its influence on fiber curl and handsheet strength properties2014In: International Mechanical Pulping Conference, IMPC 2014, 2014Conference paper (Refereed)
    Abstract [en]

    The effect on fiber and sheet properties has been compared for two different low consistency (LC) refiners in two TMP mills. One of the LC-refiners (CF 82) was running as second stage in the main line and the other (TF58) was running as second stage in the reject line. The development of fiber and strength properties was very similar for the two cases. Both disintegration in the laboratory and LC- refining decreased the fiber curl and increased the tensile index in a similar way. The effects of disintegration and LC-refining were additive.

  • 4.
    Ferritsius, Rita
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Stora Enso Paper Kvarnsveden Mill.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper.
    Ferritsius, Olof
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Rundlöf, Mats
    Capisco, Norrköping.
    Daniel, Geoffrey
    SLU, Dept. of Forest Products/Wood Science, Uppsala.
    Mörseburg, Kathrin
    Paper and Fibre Research Institute (PFI), Trondheim Norway.
    Fernando, Dinesh
    SLU, Dept. of Forest Products/Wood Science, Uppsala.
    Development of Fiber Properties in Full Scale HC and LC Refining2016In: TAPPI conference proceedings, TAPPI Press, 2016Conference paper (Refereed)
  • 5.
    Ferritsius, Rita
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Stora Enso Paper Kvarnsveden Mill, Borlänge.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper, Norrköping.
    Ferritsius, Olof
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Rundlöf, Mats
    Daniel, Geoffrey
    Mörseburg, Kathrin
    Fernando, Dinesh
    Development of fibre properties in mill scale high- And low consistency refining of thermomechanical pulp (Part 1)2020In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 35, no 4, p. 589-599Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to evaluate changes in fibre properties with high (HC)- and low consistency (LC) refining of TMP and determine how these contribute to tensile index. Two process configurations, one with only HC refining and another with HC refining followed by LC refining were evaluated in three TMP mainline processes in two mills using Norway spruce. An increase in tensile index for a given applied specific energy was similar for all LC refiners in the three lines, despite differences in the fibre property profiles of the feed pulps. Compared with only HC refined pulps at a given tensile index, HC+LC refined pulps had greater fibre wall thickness, similar fibre length, strain at break and freeness, but lower light scattering coefficient, fibre curl and external fibrillation. The degree of internal fibrillation, determined by Simons' stain measurements, was similar for both configurations at a given tensile index. The results indicate that the increase in tensile index in LC refining is largely influenced by a decrease in fibre curl and in HC refining by peeling of the fibre walls. Compared at a given tensile index, the shive content (Somerville mass fraction) was similar for both HC+LC and HC refining. 

  • 6.
    Joelsson, Tove
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. MoRe Research.
    Sandberg, Christer
    Holmen Paper.
    Norgren, Sven
    MoRe Resarch.
    Alamin, Idris
    MoRe Resarch.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Fibre morphology affects the bonding and densification of hot-pressed thermomechanical pulp-based paper2022In: Proceedings of the International Mechanical Pulping Conference, 2022, p. 142-148Conference paper (Other academic)
    Abstract [en]

    A successful way to increase the strength properties for pulps based on lignin-rich fibres is to compress the fibre structure at high temperature by means of hot-pressing technology. The fundamental knowledge of how the fi-bre morphology influences the mechanical properties when a paper sheet is hot-pressed is still scarce. Paper sheets based on thermomechanical pulp (TMP) produced with single disc and double disc refiners were compared. The effect of degree of refining was studied as well as the effect of fibre shapes by fractionating pulp with hydrocyclones. Additionally, the effect of fines was studied. All pulps were produced at the Holmen Bra-viken Mill, Norrköping, Sweden with Norway Spruce (Picea abies) as raw material. Handsheets (100 g/m2) with 62% ± 3 dryness were hot-pressed at temperatures up to 260°C at a pressure around 8MPa. The hot-press-ing increased both dry and wet strength for all pulps studied. This was true even for pulps with low fines con-tent and low refining energy. Even thick-walled fibres normally giving lower strength showed an increase of 100% when hot-pressed. In summary, hot-pressing technology can make it possible to use different TMPs to produce strong packaging materials for use in dry and wet conditions.

  • 7.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Hildén, Lars
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Fernando, Dinesh
    SLU.
    Daniel, Geoffrey
    SLU.
    Mill scale experiences of combined low dosage sulphite pre-treatment and high intensity refining of spruceManuscript (preprint) (Other academic)
  • 8.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Hildén, Lars
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Fernando, Dinesh
    SLU.
    Daniel, Geoffrey
    SLU.
    Mill scale experiences of combined sulphite pre-treatment and high intensity refining of spruce2011Conference paper (Other academic)
  • 9.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen AB.
    Paulsson, Magnus
    Akzo Nobel Pulp and Performance Chemicals AB.
    Sandberg, Christer
    Holmen Paper AB, Norrköping.
    Svensson-Rundlöf, Eva
    Holmen Paper AB, Norrköping.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Low dosage sulfite pretreatment at different refining temperatures in mill scale TMP production2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 1, p. 59-69Article in journal (Refereed)
    Abstract [en]

    The effects of low dosage sodium sulfite ( Na2SO3) pretreatment (0, 0.6 and 1.2% on bone dry wood, pH 9) at two different refining temperatures (4.6 and 6.4 bar(g) refiner housing pressure) were evaluated for production of thermomechanical pulp with a double disc refiner in mill scale using Norway spruce wood at Braviken paper mill (Holmen Paper AB, Sweden). The sulfonate content of the pulps was not affected by the different refining temperatures and was 0.29% (as Na2SO3 equivalents) for the highest sulfite addition.

    Tensile index at constant SEC was increased by 3.2 Nm/g when the refining temperature was increased, and by 8.6 Nm/g when 1.2% sodium sulfite was added. The effects were additive and led to an increase in tensile index of similar to 12 Nm/g at constant SEC when combined and would enable a reduction in SEC of 380 kWh/bdt (similar to 20%) to similar tensile index. The degree of delamination and internal fibrillation of the fibers was increased by both increased refining temperature and sulfite addition.

    Pulp brightness was slightly reduced (<= 0.4% ISO) by increased refining temperature and increased (2-3% ISO), when sodium sulfite was added. Spectra of reflectance factors (360-740 nm) were used to study the optical properties of produced pulps.

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  • 10.
    Nelsson, Erik
    et al.
    SLU.
    Sandberg, Christer
    Hildén, Lars
    Daniel, Geoffrey
    SLU.
    Pressurised compressive chip pre-treatment of Norway spruce with a mill scale Impressafiner2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, ISSN 0283-2631, Vol. 27, no 1, p. 056-062Article in journal (Refereed)
    Abstract [en]

    Mill scale trials were performed to evaluate pressurised compressive chip pre-treatment with the Impressafiner installed in one of the thermomechanical pulp lines at Braviken paper mill (Holmen Paper AB). The aim of the study was to determine if earlier reported effects of the Impressafiner pre-treatment on spruce chips from pilot scale trials (i.e. energy reduction and extractives removal) could also be attained with the mill scale Impressafiner.The mill scale Impressafiner pre-treatment resulted in partial disintegration of chips into a material consisting of fragmented chips with cracks running along the longitudinal fibre axis. Splits or evidence for weaknesses were observed between the primary and secondary fibre walls of pre-treated chips. An increase in water uptake for pre-treated chips was also observed. The extractive content was reduced by up to 24% for pulps produced with pre-treated chips compared to pulps from untreated chips. Pulp produced from pre-treated chips had higher tensile- and tear indices, elongation and light scattering and lower freeness compared to pulps from untreated chips produced with the same total specific energy consumption. The total specific energy needed to reach a tensile index of 47 Nm/g was reduced by 120 kWh/bone dry ton (6%) with Impressafiner pre-treatment. A smaller refiner plate gap was needed to reach the same specific energy consumption for pre-treated chips compared to untreated chips.

  • 11.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Svensson-Rundlöf, E
    Muhic, D
    Engberg, Birgitta A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Substantially improved energy efficiency in mechanical pulping by new feeding segment design and low dosage sulfonation in mill scaleArticle in journal (Refereed)
  • 12.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Svensson-Rundlöf, Eva
    Holmen Paper AB, S-60188 Norrkoping, Sweden.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Fernando, Dinesh
    Swedish Univ Agr Sci, Dept Forest Prod Wood Sci, S-75007 Uppsala, Sweden.
    Daniel, Geoffrey
    Swedish Univ Agr Sci, Dept Forest Prod Wood Sci, S-75007 Uppsala, Sweden.
    Low dosage sulfite pretreatment in a modern TMP-line2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 4, p. 591-598Article in journal (Refereed)
    Abstract [en]

    The effects of low dosage sulfite pretreatment combined with modern high consistency double disc refining were evaluated for production of thermomechanical pulp in a mill scale trial using Norway spruce wood at the Braviken paper mill (Holmen Paper AB, Sweden). Spruce wood chips were mechanically pretreated in an Impressafiner before impregnation with different dosages (0-1.2%) of sodium sulfite (Na2SO3) at pH 9. Approximately 23% of the added sulfite was converted to sulfonate groups in pulp, resulting in a sulfonate content of 0-0.28% (as Na2SO3). The low dosage sulfite addition increased tensile index, elongation, density, brightness and decreased shive content, light scattering and light absorption coefficients when compared at equal specific energy consumption (SEC). The increase in tensile index was proportional to dosage of sulfite. Further analyses showed that low dosage sulfite addition did not affect the distribution of the Bauer-McNett fractions nor the fibre length for pulps refined with equal SEC. However, the low dosage sulfite addition increased fibre delamination/internal fibrillation (D/IF). With the addition of 1.2% Na2SO3, it was possible to produce pulp with a tensile index of 47 Nm/g using ~320 kWh/bdt (~15%) lower refining energy, compared with pulps produced without sulfite addition.

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  • 13.
    Nelsson, Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Svensson-Rundlöf, Eva
    Muhic, Dino
    Valmet AB.
    Rohdén, Lennart
    A. Engberg, Birgitta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Improved energy efficiency in thermomechanical pulping through co-optimixation of intensity by segment design and wood softening by sulfonation2014In: International mechanical pulping conference IMPC 2014, 2014Conference paper (Other academic)
    Abstract [en]

    A mill scale trial was performed where chips were mechanically pretreated and impregnated with sodium sulfite (<7.2 g/kg). Pretreated chips were refined in two parallel double disc refiners (RGP68DD) using two different conditions: Turbine™ segment at higher production rate (higher intensity) and Low Shive™ segment at normal production rate (lower intensity). By combining the Turbine segments with chip pretreatment using a sodium sulphite charge of 3.6 g/kg it was possible to reduce the specific energy consumption by 15%, while maintaining pulp properties, compared with the lower intensity refining without pretreatment.

  • 14.
    Rubiano Berna, Jorge Enrique
    et al.
    University of British Columbia, Vancouver, Canada.
    Sandberg, Christer
    Holmen Paper AB, Bravikens pappersbruk, Norrköping, Sweden.
    Martinez, D. Mark
    University of British Columbia, Vancouver, Canada.
    Olson, James A.
    University of British Columbia, Vancouver, Canada.
    Theoretical Study of Systems Composed of Low Consistency Refining and Pressure Screening2018In: IMPC 2018, Trondheim, Norway, 2018Conference paper (Refereed)
    Abstract [en]

    The main objective of this work is to study the LC rening of mechanical pulps from system-design point of view. Mathematical models that describe bre length distribution changes were used to develop aframework capable of simulating LC rening { pressure screening systems. Specically, pressure screening models and comminution models for LC rening that are available in literature together with heuristic and a developed correlation to predict rening power were implemented in MATLAB Simulink toolbox.Later on, this same environment was used to simulate three basic rening systems found in TMP mills. In this study, each considered system was composed of a single rener and single pressure screen arranged in dierent congurations. Performance curves of length-weighed mean bre length were generated from simulation results andused to assess each system behaviour in terms of rener gap, reject ratio and rener power. The impact of some design aspects such as rener size, recirculation and reject ratio were also described. Furthermore,comparisons between systems and some basic recommendations and suggested applications are made. This theoretical framework was compared to industrial-scale data from a TMP mill sub-system. Simulation results showed good agreement with real data, where relative errors between 6-18% on the predicted variables were observed.

  • 15.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen paper.
    Fibre development in an intensified mechanical pulping process2021In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 75, no 9, p. 824-837, article id 0242Article in journal (Refereed)
    Abstract [en]

    Mechanical pulp for printing paper can be produced with a process that involve much less equipment and that require much lower specific energy compared to conventional processes. Even though common evaluation methods, e.g. handsheet testing, have shown that the pulp quality is similar for the simplified and the conventional processes, it is not known how fibre properties, at the microscopic level, is developed with the simplified process. In this mill scale study, the fibre properties attained with an "intensified"mechanical pulping process, consisting of single stage high consistency double disc refining followed by two stage low consistency refining and no reject treatment was investigated. The simplified process was compared to a process with a reject system. The simplified process rendered fibres with higher degree of fibrillation, higher share of axial splits, lower fibre wall thickness but slightly lower length than the conventional process. The fibrillar fines size distribution of the two processes was different. The conventional process generated more of small fibrillar fines which probably explains the higher tensile index at given density for that process. The results show that it is possible to simplify the production process for mechanical pulp and reduce the specific energy with over 700 kWh/adt.

  • 16.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Process intensification in mechanical pulping: Reduced process complexity and improved energy efficiency2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work shows that, for newsprint quality grades, the production processes for mechanical pulp can be simplified, and the specific electrical energy demand can be reduced with around 600 kWh/ton (30%). The purpose of the work is to demonstrate how the production cost for mechanical pulps can be decreased through increased energy efficiency and reduced number of unit operations. The idea was to improve the main line refining conditions so that no additional fibre development or shive reduction is needed and thereby, the normal screening and rejects treatment system could be omitted.

    Mechanical pulp is used to produce a variety of products, where the two largest categories are printing papers and paperboard for packaging. The pulp is mainly produced by the breakdown of wood chips between rotating metal discs in machines called refiners with the product and process generally referred to as thermomechanical pulp(ing) (TMP). The refiner process requires high specific electrical energy to separate and develop the fibres to a pulp intended for the production of printing papers. Today, many processes need over 2000 kWh/ton of refining energy plus 200-300 kWh/ton of auxiliary energy (to drive pumps, agitators, screw conveyors, screens, presses, etc.).

    During the last two decades of the 20th century, the chemical processing industry underwent a transformation. The process development changed from being unit operation focused to function focused. The result is more compact processes with less equipment, higher yield and lower energy demand. When the development is made in an innovative way with such large effects on process performance, it is referred to as process intensification. My work is inspired by the concepts of process intensification, especially the striving for more compact processes with higher efficiency. 

    This work is focused on mechanical pulp, intended for the manufacture of printing paper, produced in refiners with Norway spruce (Picea abies) as raw material. However, this approach could also be applied to mechanical pulp production in integrated paperboard mills and also using other raw materials e.g., pines or hardwoods. The investigated pulps and processes in this work are mainly intended for uncoated paper grades (newsprint, improved newsprint and book paper) printed by the offset printing process. In all studies, the pulps have been produced with full scale mill equipment and evaluated using laboratory measurements. However, in two studies, the produced pulps were evaluated on paper machines and at printing houses.

    A large number of process concepts have been evaluated in which different approaches have been used to reduce the specific energy and, in some cases, improve pulp quality. The approaches include:

    1.     Impressafiner chip pretreatment 

    2.     Primary high consistency (HC) refiner type (DD, RTS, CD, SD)

    3.     Addition of low doses of sodium sulphite 

    4.     Increased refining temperature (housing pressure)

    5.     Refiner segments and centre plate design

    6.     Increased production rate

    7.     Low consistency (LC) refining in different process positions and in combination with different HC refiner types

    The separate effects of all these techniques have not been evaluated systematically neither have potential synergistic effects of all possible combinations been investigated. Even though a large number of combinations of unit operations have been studied, the emphasis has been on trying to do as much fibre development as possible in a single HC refining stage.

    The mill trials with spruce as raw material have shown that a low shive content and appropriate fibre development can be attained in a process without separate treatment of long fibres. High intensity primary stage refining (RTS and DD) was necessary to reach a low shive content at a low specific refining energy (SRE), with DD refiners appearing to be the most suitable for simplified processes. DD and RTS refining produced pulps with fibres exhibiting a higher degree of external fibrillation and share of split fibres than SD refining. DD refining produced fibres with lower cell wall thickness and higher light scattering at given fibre length than RTS refining. The lowest specific refining energy was attained for one of the trials using the process, denoted as S:HT:DD-LC-LC, consisting of DD refining at increased production rate, 18 adt/h, increased housing pressure, 6.6 bar(g), and with 5 kg/adt sodium sulphite added to the chips immediately  before the refiner. After DD refining the pulp was refined in two LC refining stages. This process required only 1280 kWh/adt SRE to reach a tensile index of 52 Nm/g (Rapid-Köthen). This is 900 kWh/adt lower than the final pulp for newsprint based on SD HC refining, and over 500 kWh/adt lower than Scandinavian BAT processes (2014). Additionally, the auxiliary energy was around 150 kWh/adt lower for the processes without a conventional rejects treatment system. At 52 Nm/g tensile index, the light scattering coefficient was 2-3 m2/kg higher, and the length-weighted average fibre length was around 0.1 mm lower for this process than for SD TMP final pulp. The fibre bonding, indicated by density, tensile index and Z-strength of fibre fraction handsheets, was similar or higher for the S:HT:DD-LC-LC process than the reference SD TMP process with a rejects treatment system. 

    Other interesting process configurations, with somewhat lower efficiencies, included:

    1.     Impressafiner pretreatment of the chips with sodium sulphite before DD refining, with or without subsequent LC refining. Chip pretreatment with the Impressafiner enabled operating the DD refiner at higher intensity (feeding segments and increased production rate) without significant loss of quality and LC refining enabled increased production rate which increased the overall efficiency.

    2.     RTS-SD refining with sodium sulphite added before the second stage SD refiner referred to as RTS-S:SD. The pulp from the RTS-S:SD process had similar fibre length as the S:HT:DD-LC-LC process but lower light scattering coefficient.

    3.     A single-stage DD refiner operating at 15.5 adt/h and 4 bar(g) housing pressure (no sodium sulphite addition), which produced pulp with lower fibre length but higher light scattering coefficient than the S:HT:DD-LC-LC process. 

    Two simplified processes were evaluated on paper machines and in printing houses. The first, denoted DD-LC-F, involved a combination of DD primary refining followed by LC refining and fractionation (screening). The screen rejects were mixed with the main line DD pulp before the LC refiner. The second process was the CPT:S-DD-LC process (№1 above). Good runnability was attained both on the paper machines and in the offset printing presses and the paper quality was similar to the reference paper.

    For printing paper applications, the proportion of fibre development in LC refining should preferably be relatively low, since it was shown that LC refiners have limited capacity to reduce fibre wall thickness and thereby develop light scattering and fibre fraction Z-strength.

    Explicit effects on the number of unit operations and production cost have not been evaluated in this work, but clearly both investment and variable costs as well as fixed costs can be reduced with a simplified process.

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  • 17.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Effect of flow recirculation on pulp quality and energy efficiency in low consistency refining of mechanical pulp2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 2, p. 230-233Article in journal (Refereed)
    Abstract [en]

    The effect of pulp flow recirculation on energy efficiency and pulp properties development in low consistency refining of TMP has been studied. Trials were made with TwinFlo 58 refiners in two mills in Sweden. The refiners were operated at constant specific refining energy but different flow conditions. No effect of recirculation was seen on refining energy efficiency, pulp quality or fibre wall delamination/internal fibrillation. At high degree of recirculation though, a somewhat larger fibre length reduction was seen. This means that a large degree of recirculation can be used to attain a high specific energy in one stage low consistency refining, without significant negative effects on fibre properties. If a high specific energy input is desirable, it is more cost effective to install one large refiner with recirculation compared to several small without recirculation in series. When recirculation was increased by means of increased flow through the refiner, the outlet pressure dropped. The lower pressure drop over the refiner probably decreased the internal recirculation between rotor and stator, which could explain the observation that there was little effect on fibre development by recirculation. This means that at certain conditions the distribution in fibre treatment might not increase so much when the outer recirculation is increased, since the internal recirculation might be reduced simultaneously.

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  • 18.
    Sandberg, Christer
    et al.
    Holmen Paper AB.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    LC refining combined with screen fractionation – Reduction of system complexity for mechanical pulping2018In: IMPC 2018, Trondheim, Norway, 2018Conference paper (Refereed)
    Abstract [en]

    Process intensification - a process development method used in the chemical process industry has been appliedto mechanical pulping process design. Process intensification is characterized by significant reduction of energyconsumption and process complexity.A process with single stage high consistency (HC) refining followed by low consistency (LC) refining andscreening was evaluated in mill trials at the Holmen Paper Braviken mill, Sweden. After LC refining, pulp wasscreened and the reject was fed back to LC refining. The process is called HC-LC-S. Two different HC primaryrefiner types were evaluated – single disc (SD) and double disc (DD).High intensity DD chip refining was more suitable than single disc refining for the process due to higher lightscattering and lower shives content of the final pulp. It was also easier to reach high enough tensile index beforeLC refining with the DD refining. The DD-LC-S process required 1940 kWh/adt total specific energy for newsgrade TMP, which was 300 kWh/adt lower than the reference TMP line; DD chip refining and HC rejectrefining. The auxiliary specific energy was reduced with 100 kWh/adt.Six unit operations and three chests with agitators and pumps were omitted compared to a conventional TMPline.

  • 19.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper AB, Norrköping.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Low Consistency Refining Combined with Screen Fractionation: Reduction of Mechanical Pulping Process Complexity2019In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, no 1, p. 882-894Article in journal (Refereed)
    Abstract [en]

    Process intensification is a process development methodology aimed at a considerable reduction in the energy consumption and process complexity. The approach has been applied to mechanical pulping process design. A process denoted as HC-LC-S consisting of single stage high consistency (HC) refining, followed by low consistency (LC) refining and screening was evaluated in mill trials at the Holmen Paper Braviken Mill in Sweden. After LC refining, the pulp was screened, and the reject fraction was fed back to LC refining. Two HC primary refiner types were evaluated, namely single disc (SD) and double disc (DD). Double disc chip refining was more suitable than SD refining for the HC-LC-S process because of the higher light scattering and lower shives content of the final pulp. The tensile index and shives content of the pulp produced with the DD-LC-S process was similar to that of the reference process, consisting of single stage DD refining and HC reject refining, but the fibre length and light scattering were somewhat lower. The specific refining energy was approximately 200 kWh/adt lower for the DD-LC-S process compared with the reference. Additionally, the auxiliary specific energy was 100 kWh/adt lower for the HC-LC-S processes, since a number of equipment units were omitted.

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  • 20.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper, Norrköping.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Low consistency refining of mechanical pulp - system design2017In: TAPPI Journal, ISSN 0734-1415, Vol. 16, no 7, p. 419-429Article in journal (Refereed)
    Abstract [en]

    Many mechanical pulping mills use low consistency (LC) refining for energy efficient fiber development. In this study, energy efficiency and pulp quality were evaluated for six processes, of which four included LC refining. We studied two different types of chip refiners - single disc (SD) and double disc (DD) - with LC refining in the main and reject lines. All process combinations have been used in the Holmen Paper Braviken mill, Sweden, to make thermomechanical pulp for printing papers. LC refining was more energy efficient than high consistency (HC) refining at certain tensile index increases in all evaluated combinations. LC refining in the main line had somewhat higher energy efficiency than did LC refining in the reject line. The type of chip refiner (DD or SD) did not affect the efficiency or pulp property development in LC refining. The process with a combination of DD chip refining and LC refining had the highest energy efficiency (tensile index at certain specific energy consumption). All processes with LC refining produced pulp with somewhat lower light scattering and fiber length than did the corresponding system with only HC refining. Thus, for printing papers, the best combination was LC refining with DD chip refining. LC refiners seem to have a narrow range in specific energy for maximum energy efficiency and a good balance between tensile index increase and fiber length reduction. Much higher specific energy was applied on reject pulp. However, the reject share was only around 30%. The LC refining specific energy, based on main line production, was around 80 kWh/air-dried metric ton (a.d. metric ton), whereas up to 180 kWh/a.d. metric ton was applied in main line.

  • 21.
    Sandberg, Christer
    et al.
    Holmen Paper AB, Norrköping.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Process intensification in mechanical pulping2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 4, p. 615-622Article in journal (Refereed)
    Abstract [en]

    Process intensification is a term used in the chemical process industry for major improvements in the process design leading to radical changes in process complexity, equipment size and efficiency. We suggest that a similar approach is applied in the pulp and paper industry. We have focused on the production of mechanical pulp, but a similar approach can be applied to other areas within the pulp and paper industry. Inspired by process intensification methodology, we suggest five principles for development of the mechanical pulping process. Three fundamental principles; 1. Break up the wood and fibre wall structure in the right positions. 2. Give each fibre, of certain morphology, the same processing experience. 3. Optimize the applied mechanical forces and the physiochemical state of the wood and fibre material.  and two system oriented principles; 1. Select wood raw material based on final product specifications. 2. Design the process to facilitate observability, controllability and maintenance. Implications of these principles on process design and future challenges for mechanical pulping are discussed.

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  • 22.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Berg, Jan-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    System Aspects on Low Consistency Refining of Mechanical Pulp2016In: TAPPI 2016 International Mechanical Pulping Conference (IMPC), TAPPI Press, 2016, Vol. 1, p. 485-495Conference paper (Refereed)
    Abstract [en]

    Several combinations of high consistency (HC) and low consistency (LC) refiners were evaluated both in main line and reject line for production of pulp for printing papers. HC-LC processes were compared with processes with only HC refining. Processes with two different types of chip refiners were studied – single disc (SD) and double disc (DD). All process combinations were evaluated during continuous production in the Holmen Paper Braviken mill, Sweden. The purpose of this work was to evaluate energy efficiency and pulp quality for the processes.

    LC refining was more energy efficient than HC refining for certain tensile index increase in all evaluated combinations. The highest energy efficiency was attained when LC refining was utilized in main line, but the difference was small compared to application on reject. Much higher specific energy was applied on reject pulp, but since the reject share was only around 30%, the LC refining specific energy, based on main line production, was around 80 kWh/air dry ton (adt) whereas up to 180 kWh/adt was applied in main line.

    The combination of DD chip refining and LC refining had the highest energy efficiency (tensile index at certain specific energy consumption) and produced pulp with somewhat lower fibre length but higher light scattering and lower shives content compared to a line with only SD HC refining. Thus, for printing papers it seems beneficial to combine LC refining with high intensity HC chip refining. All processes with LC refining had lower light scattering and fibre length compared to the corresponding system with only HC refining.

  • 23.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper.
    Ferritsius, Olof
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Ferritsius, Rita
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. StoraEnso.
    Energy efficiency in mechanical pulping2017Conference paper (Refereed)
  • 24.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen paper.
    Ferritsius, Olof
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Ferritsius, Rita
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Stora Enso.
    Energy efficiency in mechanical pulping-definitions and considerations2021In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 36, no 3, p. 425-434, article id 0013Article in journal (Refereed)
    Abstract [en]

    Production of mechanical pulps requires high specific electrical energy compared to many other attrition processes. In Scandinavia, the lowest specific refining energy for production of thermomechanical pulp is around 1800 kWh/t for newsprint quality, which is roughly 60 times higher than for crushing of stone to a similar size distribution. The high specific energy demand for refining has naturally motivated large efforts in the search for improved efficiency. It is always practical to be able to quantify improvements in efficiency for comparison of process designs and of different machine types. However, there is no commonly accepted definition of efficiency for mechanical pulping processes. In published work within mechanical pulping, energy efficiency has been presented in different ways. In this paper, we discuss definitions of energy efficiency and aspects that ought to be considered when energy efficiency is presented. Although focus of this work is on energy efficiency for refiner processes, the principles can be applied to other types of mechanical pulping processes such as stone groundwood. 

  • 25.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper, Norrköping.
    Hill, Jan
    QualTech, Tyringe.
    Jackson, Michael
    Michael Jackson Consulting Inc., Vancouver, Canada.
    On the development of the refiner mechanical pulping process - A review2020In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 35, no 1Article in journal (Refereed)
    Abstract [en]

    This paper is a review of the development of the mechanical pulping process with focus on refiner-based processes. The intention is to provide an overview of the trends and the major advances in the development of the mechanical pulping (MP) process. The focus is on the development of the entire MP process, rather than the refiner as such. However, when discussing the MP process development, it is inevitable to consider the development of the refiner unit operation briefly. Processes for printing papers based on softwood is mainly discussed, but board processes are discussed briefly as well. 

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  • 26.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Lundfors, Mikael
    Valmet.
    Lönngren, Karl
    Valmet.
    New centre-plate design improves DD refiner performance2022In: International Mechanical Pulping Conference, Vancouver, Canada, 2022, 2022, p. 63-68Conference paper (Other academic)
  • 27.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen Paper.
    Lundfors, Mikael
    Valmet.
    Lönngren, Karl
    Valmet.
    New centre-plate design improves DD refiner performance2022In: Proceedings of the International Mechanical Pulping Conference, 2022, p. 63-68Conference paper (Other academic)
    Abstract [en]

    Valmet has developed a new centre plate, for the RGP68DD refiner, which minimise the free volume in the centre of the refiner. The new centre plate has been evaluated in trials with Norway spruce as raw material for production of TMP for printing paper at the Holmen Braviken Mill, Norrköping, Sweden. The new and old centre plate was compared by generating refining curves both by changing gap at constant production rate and by increasing production rate at constant gap. When the production rate was increased from 13 to 19 adt/h in the trial with the new centre plate, the power and gap varia-tions were reduced by around 70%. The new centre plate did not affect tensile index and shives content at given specific energy. However, the fibre length at given ten-sile index was somewhat higher and the light scattering coefficient lower with the new centre plate, which might be an effect of increased blow line consistency and less power variations. The large improvement of refiner sta-bility and the increased fibre length opens up for seg-ment design development aiming at larger specific en-ergy reduction.

  • 28.
    Sandberg, Christer
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Sundström, Lars
    Andersson, Stefan
    Nelsson, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    New TMP-line improves pulp quality and reduces energy consumption2011Conference paper (Other academic)
  • 29.
    Sund, Johan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen paper.
    Sandberg, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Holmen paper.
    Karlström, Anders
    Chalmers.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    The effect of process design on refiner pulp quality control performance2021In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 36, no 4, p. 594-607Article in journal (Refereed)
    Abstract [en]

    In this study, the effect of process- and online analyser configuration on pulp quality control is explored. The following parameters were included: analyser sampling interval, time delay, measurement error magnitude, and latency chest residence time. Using different values of parameters in a process model, a range of configurations were constructed. For each configuration, the achievable control performance was evaluated using an optimization approach. PI controller settings were chosen based on minimization of the integrated absolute error (IAE) in pulp quality after an input step disturbance. The results show that reducing the sampling interval improves performance also when the interval is smaller than the chest residence time or the analyser delay. Moreover, reducing the chest residence time can reduce the IAE by up to 40 %. However, reducing the residence time to lower than 1/3 of the sampling interval does not improve performance. Further improvement is possible if the analyser delay is reduced. The compromise between reducing the IAE and avoiding creating variation by acting on measurement error has a strong influence on the results. In conclusion, pulp quality control performance can be improved significantly by making changes to the studied configuration parameters. 

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  • 30.
    Sund, Johan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Sandberg, Christer
    Holmen Paper.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Engstrand, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Continuous online fibre analysis enables improved pulp quality estimation and control2022In: Proceedings of the International Mechanical Pulping Conference, 2022, p. 99-106Conference paper (Other academic)
    Abstract [en]

    In this work, high-rate fibre analysis has been used for direct feedback control of pulp quality by application of a new control strategy for a two-stage refining process in the Holmen Hallsta mill, Sweden. The application is based on control of pulp freeness, estimated from the continuous fibre analysis results from a BTG Single Point Morphology ana-lyzer. The goal was to create a robust and simple control strategy. The new strategy includes control of plate gap, con-sistency and the hydraulic force difference between the stages. Expressed as standard deviation, the freeness and av-erage fibre length variations were reduced by 50% and 25% respectively. The small size of the pulp chest in this process also benefits stronger feedback control. Long-term operation suggest that high-rate fibre analysis can be used to reduce faster quality variation.

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