Macro Flow in a Pressure Screen, 1995 Pulping Conference Proceedings

Jouko Niinimäki

University of Oulu

Pressure screening in nowdays the dominant type of cleaning and fractionating fiber suspension in stock preparation. There are thousands of pressure screens in use today in United States. Different screen manufactures provide tens of different types of screening systems for different purposes. Despite very good results in screening fiber suspension in the pressure screens, we have no explicit knowledge of actual mechanism affecting screening results. Research and devel-opment of screening are based principally on experimental design, where different screen constructions are compared. There is only a little published information about the basic principles of screening. The behaviour of pulp fibers in a slotted pressure screen is investigated in five different parts. The first part of this study examines the macro flows and mixing in the screen basket. The investigation method used is a high speed video record-ing at low pulp consistency and the radioactive tracer method with high consistency pulp. The experiments are carried out in the small pressure screen, which is used widely in industry for broke screening or fiber recovery.