The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Fibres and Energy from Wheat Straw by Simple Practice

Anja Leponiemi

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Chemical Technology for public examination and debate in Auditorium Puu2 at the Aalto University School of Chemical Technology (Espoo, Finland) on the 5th of August 2011 at 12 noon.

Overview in PDF format (ISBN 978-951-38-7744-6)   [1157 KB]
VTT Publications 767, ISSN 1455-0849

Dissertation is also available in print (ISBN 978-951-38-7743-9)
Copyright © 2011 VTT Technical Research Centre of Finland
VTT Publications 767, ISSN 1235-0621
VTT-PUBS-767

Abstract

The overall purpose of this work is to evaluate the possibilities of wheat straw for fibre and energy production and address the question of whether or not it is possible to develop a cost-effective process for producing good quality pulp from wheat straw for current paper or paperboard products. In addition, in light of the green energy boom, the question of whether fibre production could give added value to energy production using wheat straw is addressed.

Due to the logistics of the bulky raw material, the process should be applied on a small scale that determines the requirements for the process. The process should be simple, have low chemical consumption and be environmentally safe. The processes selected for the study were based on an initial hot water treatment. Actual defibration in the "chemical" approach was then performed using a subsequent alkaline peroxide bleaching process or in the "mechanical" approach through mechanical refining. In both approaches, energy can be produced from lower quality material such as dissolved solids or fines.

In this work, one of the primary aims besides the development of the abovementioned process is to investigate the chemical storage of wheat straw which decays easily between harvesting periods and examine its effects on pulping and pulp properties. In addition, the aim of this work is to determine the market potential for non-wood pulp and evaluate non-wood pulp production.

The results showed that the "chemical" approach produced fibres for printing and writing. The quality of the pulp was relatively good, but the chemical consumption at the target brightness of 75% was high, indicating that a chemical recovery would be needed unless the brightness target could be significantly reduced. The "mechanical" approach produced unbleached fibres for fluting and the energy production from fines and dissolved solids generated additional income. The results also showed that it is possible to store wheat straw chemically with formic acid-based chemicals over a year without significant changes in the chemical composition. The chemical storage can be integrated with the suggested chemical or mechanical defibration process, soda pulping process or any other process utilising non-wood fibres. In China, a clear demand for non-wood-based fibres exists due to a shortage of fibre and also because of the increasing demand for bioenergy. In Europe, the competitiveness of non-wood fibre utilisation will only be established if combined with energy production.

This thesis consists of an overview and of the following 5 publications:

  1. Leponiemi, A. (2008). Non-wood pulping possibilities – a challenge for the chemical pulping industry. Appita J. 61(3), pp. 234-243.
  2. Leponiemi, A., Johansson, A., Edelmann, K. and Sipilä, K. (2010). Producing pulp and energy from wheat straw. Appita J. 63(1), pp. 65-73.
  3. Mustajoki, S., Leponiemi, A. and Dahl, O. (2010). Alkaline peroxide bleaching of hot water treated wheat straw. Bioresources 5(2), pp. 808-826.
  4. Leponiemi, A., Pahkala, K. and Heikkilä, T. (2010). Storage of chemically pretreated wheat straw – A means to ensure quality raw material for pulp preparation. Bioresources 5(3), pp. 1908-1922.
  5. Leponiemi, A., Johansson, A. and Sipilä, K. (2011). Assessment of combined straw pulp and energy production. Bioresources 6(2), pp. 1094-1104.

Keywords: non-wood fibre, wheat straw, biorefinery, hot water treatment, mechanical refining, alkaline peroxide bleaching, chemical pre-treatment, storage, assessment, pulp, energy

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© 2011 Aalto University

Last update 2011-08-15