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Improved energy efficiency in double disc chip refining
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN – Fibre Science and Communication Network)
2010 (English)Licentiate 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.

 

 

Abstract [sv]

Den höga elenergiförbrukningen vid produktion av mekanisk massa har ställtkrav på mer forskning för att elenergieffektivisera raffineringsprocessen. Som ettsteg mot en mer energi‐ och kostnadseffektiv raffineringsprocess, har HolmenPaper AB investerat i en ny tillverkning av termomekanisk (TMP) massa vidBravikens pappersbruk. Dubbeldiskraffinörerna i den nya massalinjens primäraraffineringssteget studerades i detta projekt. Det finns goda indikationer på att enminskning av energiförbrukningen är möjlig genom att studerar och optimeraraffineringparametrar såsom intensitet och temperatur. Projektets huvudmål varatt energieffektivisera det primära dubbeldiskraffineringssteget med 150 kWh/adttill motsvarande massaegenskaper, så som dragstyrka, mätt på massa efterraffinör. Tillfälle gavs också till att studera morfologiska förändringar på fibrer föratt ytterligare förstå hur massa och fibrerna påverkas av dubbeldiskraffinering ochförändringar i raffineringssystemet.Detta licentiatprojekt är en del av ett större projekt där olika tekniker för attförbättra energieffektiviteten har utvärderats i industriell skala på Holmen PaperBravikens pappersbruk. Licentiatprojektet är finansierat av KK‐stiftelsen, MetsoPaper och Holmen Paper, i samarbete med Mittuniversitetet.Fullskaleförsök gjordes på en av TMP linjerna vid Bravikens pappersbruk, därgran används som råvara. Studien utfördes på dubbeldiskraffinörerna i detprimära raffineringssteget. Malkurvor, med ökande specifik raffineringsenergi,gjordes vid olika raffineringstemperaturer, intensitet, massakoncentration ochproduktion. Resultat som erhållits från malkurvorna bekräftades med längrestudier på raffinörerna. Intensitetsmodeller och simuleringar utfördes av Juha‐Pekka Huhtanen från Tampere University of Technology.De erhållna resultaten visar på att energiförbrukningen till ett visst dragindexkan minskas genom att öka raffineringstrycket/temperaturen. Medraffineringstryck menas inlopp och hustryck i raffinören. Energibesparingen är iintervallet 80‐150 kWh/adt. Den största förbättringen kan uppnås vid lågaenergiinsatser. Massor producerade med högt tryck och temperatur och lägrespecifik energiförbrukning uppvisar liknande ultrastrukturella ytegenskaper sommassor producerade med lågt tryck och temperatur och hög specifik energi. Högttryck och temperaturer med hög specifik energiinsats gav en signifikant förbättringav delaminering/intern fibrillering av massafibrer. Dessa fibrer uppvisadebildningar av långa band‐liknande fibriller från fibrernas S2 skikt, i jämförelse medmassor tillverkade med lägre tryck och temperatur och lägre specifik energi.5Om raffineringen genomförs vid högt tryck/temperatur bevaras dragindexunder hela segmentlivslängden.Den specifika ljusspridningskoefficienten påverkades positivt av ökat tryck ochtemperatur. En orsak till detta kan vara högre intensitet som orsakas av minskadmalspalt.Ökad intensitet genom förändrad segmentdesign leder till stora ökningar i denspecifika ljusspridningskoefficienten. Samtidigt uppnås samma dragindex, lägrespethalt, lägre genomsnittlig fiberlängd och CSF vid samma specifikaenergiförbrukning.Förbrukningen av färskångan sänktes vid tillämning av högre tryck ochtemperatur i raffinören.

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet , 2010. , p. 42
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 46
Keyword [en]
thermomechanical pulping (TMP), double disc refining, high intensity
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-12979ISBN: 978-91-86073-94-7 (print)OAI: oai:DiVA.org:miun-12979DiVA, id: diva2:387536
Presentation
2010-10-28, 10:00
Supervisors
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2017-03-10Bibliographically approved
List of papers
1. Influence of temperature on energy efficiency in double disc chip refining
Open this publication in new window or tab >>Influence of temperature on energy efficiency in double disc chip refining
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2010 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 4, p. 420-427Article in journal (Refereed) Published
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.

Keyword
TMP; energy efficiency; Temperature; Pressure; Double disc refining; Segment wear; Pulp quality
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-13003 (URN)10.3183/NPPRJ-2010-25-04-p420-427 (DOI)000285701900001 ()2-s2.0-78651404683 (Scopus ID)
Available from: 2011-01-15 Created: 2011-01-15 Last updated: 2017-12-11Bibliographically approved
2. Energy efficiency in double disc refining. Influence of intensity by segment design
Open this publication in new window or tab >>Energy efficiency in double disc refining. Influence of intensity by segment design
Show others...
2011 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 3, p. 224-231Article in journal (Refereed) Published
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.

Keyword
TMP; Double disc refining; Intensity; Segment design; Energy efficiency; Segment performance simulation
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-13005 (URN)10.3183/NPPRJ-2011-26-03-p224-231 (DOI)000294524200001 ()2-s2.0-80052389573 (Scopus ID)
Available from: 2011-01-15 Created: 2011-01-15 Last updated: 2017-12-11Bibliographically approved
3. 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 surfaces
Open this publication in new window or tab >>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 surfaces
2011 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, no 6, p. 777-786Article in journal (Refereed) Published
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.

Keyword
cell wall ultrastructure; delamination/internal fibrillation (D/IF); energy efficiency; fibre development; Norway spruce; S1 layer; S2 layer; SEM; Simons' stain (SS); temperature; thermomechanical pulp (TMP)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-13006 (URN)10.1515/HF.2011.076 (DOI)000297527600001 ()2-s2.0-80053608748 (Scopus ID)
Available from: 2011-01-15 Created: 2011-01-15 Last updated: 2017-12-11Bibliographically approved

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