University of Oulu

Studies on washing in kraft pulp bleaching

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Author: Sillanpää, Mervi1
Organizations: 1University of Oulu, Faculty of Technology, Department of Process and Environmental Engineering
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.1 MB)
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Language: English
Published: Oulu : University of Oulu, 2005
Publish Date: 2005-11-15
Thesis type: Doctoral Dissertation
Defence Note: Academic Dissertation to be presented with the assent of the Faculty of Technology, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB210), Linnanmaa, on November 25th, 2005, at 12 noon
Reviewer: Professor Jorge Luiz Colodette
Professor Kaj Henricson


Washing during kraft pulping can be divided into two separate areas each with its own distinct features: namely brownstock washing and washing in bleaching. Research interest has so far concentrated mostly on investigating brownstock washing and factors affecting its efficiency. Pulp washing in bleaching, however, has been practically neglected. The basic phenomena are the same as in brownstock washing, but there are differences which have not been taken into consideration to a sufficient extent. This less explored area is the focus of this research.

In this thesis, it is shown that brownstock washing and pulp washing between bleaching stages are distinct areas with their own specific features. They differ for example in terms of the composition and molecular size of the impurities in the pulp suspension. Various process conditions, pH, temperature and so on cause further differences between washing in bleaching and brownstock washing.

The removal of specific compounds can be clearly affected by the appropriate selection of wash liquor. It is shown that the dynamic behaviour during washing is different for different compounds and depends on the properties of the wash water. The key element is to find the most harmful compounds in specific positions in bleaching and on the basis of that finding, to determine the most suitable wash liquor system.

Chemical oxygen demand (COD) is a widely used method for evaluating the washing result, but as a collective measurement variable it does not describe the actual compounds that cause the "loss" of bleaching chemicals. Studies have shown that many compounds contribute to COD load but ultimately most of them have no real effect on the bleaching result. A suggestion for more precise definition of wash loss is offered than COD.

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Series: Acta Universitatis Ouluensis. C, Technica
ISSN: 0355-3213
ISSN-E: 1796-2226
ISSN-L: 0355-3213
ISBN: 951-42-7877-1
ISBN Print: 951-42-7876-3
Issue: 228
Copyright information: © University of Oulu, 2005. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.