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High temperature CTMP from birch
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. (FSCN – Fibre Science and Communication Network)
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is intended to contribute to understanding of the chemithermomechanical pulping of birch intended for high freeness grades. It focuses on the effects that conditions during pre‐treatment, i.e. the chemical addition of sodium sulphite and sodium hydroxide and the temperature in pre‐heater, have on the energy consumption and process runnability in terms of disc clearance. Pulp properties are evaluated in regard to brightness and the relation between bulk and internal bond strength. Pilot trials showed that pre‐heating birch chips to high temperature prior to refining (HT CTMP > 140°C), facilitated defibration and considerably lowered energy consumption. This made it possible to produce pulp with very high freeness. Despite the low energy input at high pre‐heating temperature, shive content remained low or was even reduced in the high freeness range. Mill trials confirmed the positive effect of a high pre‐heating temperature on energy consumption and on pulp properties. Furthermore it was shown that the internal bond strength in sheets from birch CTMP, in terms of Scott‐Bond at a given bulk, compared well with that of Spruce CTMP. Moreover, the shive content of birch CTMP produced using the high temperature technique was lower than that of spruce CTMP at a given bulk. A new laboratory technique ʹthe shavings methodology was used in combination with multivariate data analysis to investigate the effect of various pre‐treatments on native wood brightness. This method looks directly on the changes in brightness of the green wood as such. It revealed that the brightness of green birch wood is sensitive to increases in relative humidity and temperature. It also indicated that using a relatively high pre‐heating temperature (~140–155°C) when manufacturing birch CTMP is not necessarily detrimental to pulp brightness, provided the chemical charge is properly adjusted. However, at very high temperature (>160°C), the time in the pre‐heater should be kept short. Measurement of frictional behaviour, at simulated CTMP conditions, showed that the coefficient of friction of birch was greatly affected by chemical modification. Thus extraction raised the coefficient of friction. This rise can probably be attributed to reduced lubrication by the extractive substances and to the higher moisture content in the extracted samples. Sulphonation of the birch samples with 3 % Na2SO3 and 2 % NaOH (pH 13.5) gave a local maximum around 140–155°C. The local peak may be correlated with the reduction in energy consumption when the pre‐heating temperature is increased in the production of birch CTMP. Birch wood and spruce wood are also shown to have distinct differences in frictional performance. The coefficient of friction between birch and steel is higher than that between spruce and steel. The high stiffness and density of the birch wood and differences in the amount and composition of birch and spruce extractive substances probably account for the observed variations.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2006.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 11
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-9109ISBN: 91-85317-20-9 (print)OAI: oai:DiVA.org:miun-9109DiVA, id: diva2:222375
Presentation
2006-05-10, Sundsvall, 00:00 (Swedish)
Opponent
Available from: 2009-06-08 Created: 2009-06-08 Last updated: 2009-07-13Bibliographically approved
List of papers
1. Chemitermomechanical pulp made from birch at high temperature
Open this publication in new window or tab >>Chemitermomechanical pulp made from birch at high temperature
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 216-221Article in journal (Refereed) Published
Abstract [en]

The inherent stiffness of birch wood-fibres makes birch an excellent raw material in the manufacture of high bulk pulp. By a combination of chemical impregnation of birch chips and pre-heating of the chips to high temperature prior to refining, it is possible to manufacture CTMP with very high bulk using a low energy input. Trials revealed that the high pre-heating temperature lowers the energy consumption considerably. At 500 ml CSF an increase in the pre-heating temperature from 110C to 160C reduced the energy consumption by more than 40 %. Despite the low energy input, the shive content remained low or was even reduced and the internal bond strength, in terms of Scott-Bond, compared favourably with Spruce CTMP. In summary, a high pre-heating temperature can be used to manufacture birch CTMP with very high bulk, at a low energy consumption.

Keywords
CTMP, birch, pre-treatment. pre-heating, energy consumption, paperboard, bulk, shive content.
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-3757 (URN)10.3183/NPPRJ-2006-21-02-p216-221 (DOI)000238726200008 ()2-s2.0-33745726932 (Scopus ID)4038 (Local ID)4038 (Archive number)4038 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
2. A method to optimise birch CTMP pre-treatments by direct measurement of brightness on birch wood
Open this publication in new window or tab >>A method to optimise birch CTMP pre-treatments by direct measurement of brightness on birch wood
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 3, p. 419-425Article in journal (Refereed) Published
Abstract [en]

It is challenging and quite difficult to optimise the pre-treatment of birch CTMP with respect to brightness in large-scale trials. Because of the complexity of the system, it is necessary to go beyond a two-dimensional experimental approach (where not more than two variables are varied at the same time) to find optimal conditions. This paper presents a straightforward laboratory technique that may be used to study the effects on the brightness of wood by various pre-treatments. Combining this methodology with multivariate data analysis provides a powerful tool for optimising birch CTMP pre-treatment with respect to brightness. Recommendations within the experimental domain are given.

Keywords
Birch, Brightness, Pre-heating, Pre-treatment, Sodium hydroxide, Sodium sulphite
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-8677 (URN)10.3183/NPPRJ-2006-21-03-p419-425 (DOI)000241531500018 ()2-s2.0-33750404759 (Scopus ID)
Available from: 2009-02-26 Created: 2009-02-26 Last updated: 2017-12-13Bibliographically approved
3. Frictional properties of native and chemically modified birch wood
Open this publication in new window or tab >>Frictional properties of native and chemically modified birch wood
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 325-330Article in journal (Refereed) Published
Abstract [en]

The chemithermomechanical pulping of hardwoods has attracted increasing interest in the past decade. This study investigates the frictional behavior of both native and chemically treated birch under simulated chip-refining conditions (hot saturated steam, high sliding speed). Chip pretreatment, i.e. chemical impregnation and pre-heating done when birch chemithermomechanical pulp is produced, affects energy consumption during refining; the study found that frictional forces may be an important parameter in this respect. The coefficient of friction peaks at approximately 115°C for both native and extracted birch. It was shown that sulfonating native birch decreased its coefficient of friction over the temperature range investigated (100�170°C). The coefficient of friction had a broad and flat peak in the 130�150°C temperature interval for the specimens treated with 3% sodium sulfite at pH 13.5. Furthermore, it was clear that pH had a profound influence on the coefficient of friction. A high pH lowered the coefficient of friction, likely due to well lubricated contacts. The friction arising between birch (Betula verrucosa) and steel was shown to be higher than that between spruce (Picea abies) and steel. The higher stiffness and density of the birch wood, together with a more porous bulk structure leading to rough test surfaces, are some factors possibly accounting for these high friction coefficients. Also, the differences in the amount and composition of the extractive substances in birch and spruce may contribute to the differing frictional behaviors of these species.

Keywords
Birch, Friction, Mechanical pulping, CTMP, Sodium sulfite, Sodium hydroxide, Wood extractives, Energy consumption
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-4045 (URN)10.3183/NPPRJ-2007-22-03-p325-330 (DOI)000250025000006 ()2-s2.0-34948882653 (Scopus ID)4533 (Local ID)4533 (Archive number)4533 (OAI)
Available from: 2008-09-30 Created: 2009-06-08 Last updated: 2017-12-12Bibliographically approved

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Vesterlind, Eva-Lotta

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