| Fractionation of thermomechanical pulp in pressure screening: An experimental study on the classification of fibres with slotted screen plates | ||
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The background to the research, the environment in which it took place and the hypotheses to be tested are introduced in Chapter 1.
The literature review in Chapter 2 describes some principles of pressure screen and screen plate design and introduces screening parameters and their effect on performance. Some basic pressure screening performance equations and their interrelations are introduced and the ability of pressure screens to fractionate pulp according to different fibre properties is also reviewed.
The numerical characterisation methods available for analysing the fractionation of pulp are presented in Chapter 3.
Chapter 4 describes the experimental work involved in this thesis. Firstly, the preliminary work concerning analytical methods for characterising fractionation is presented. Consistency, Canadian standard freeness, Bauer-McNett fractions, optical fibre length and image analysis are considered, the modelling of Bauer-McNett fractions by means of optical fibre length distributions and freeness values is discussed and some equations for expressing coarseness are introduced. Secondly, the experimental arrangement for the primary work concerning fractionation by means of slotted pressure screening is introduced. The primary work consists of four parts: the effects of operating parameters on fractionation, the effects of screen plate design, the role of fibre coarseness and the role of sampling in the experimental work.
The results of the experimental work are presented in Chapter 5. The effects of operating parameters and screen plate design on pulp fractionation measured in terms of Bauer-McNett fractions and freeness are considered, together with the role of fibre coarseness in fractionation and the role of sampling in experimental testing.
The above results and their relevance are discussed in Chapter 6, the most important findings are summarised in Chapter 7, and some thoughts about topics for future work on fractionation and the characterisation of fibre properties are put forward in Chapter 8.