CHEMICAL AND PROCESS ENGINEERING 29, 43–60 (2008) D. ASENDRYCH 1* , M. FAVRE-MARINET 1 , F. JULIEN SAINT AMAND 2 , G. WOJCIECHOWSKI 2* NUMERICAL STUDIES ON THE EXTRUSION OF VISCO-ELASTIC PARTICLES THROUGH SLOTS IN A SCREENING PROCESS 1 Laboratoire des Ecoulements Geophysiques et Industriels, Grenoble University, CNRS-UJF-INPG, BP 53, 38041 Grenoble Cedex 9, France 2 Centre Technique du Papier, Grenoble, BP 251, 38044 Grenoble Cedex 9, France The paper is devoted to the optimisation of contaminants removal from cellulose fibres suspension during paper recycling. The behaviour of viscoelastic particles (originating from adhesive tapes and labels entering recycling loops) in the screen is studied numerically upon varying key parameters of the process showing their impact on the separation efficiency. Badano optymalizacjĊ procesu usuwania zanieczyszczeĔ z zawiesiny włóknistej w trakcie przetwór- stwa makulatury. Zachowanie lepkosprĊĪystych cząsteczek (których Ĩródłem są samoprzylepne taśmy i naklejki) na sicie sortownika poddano analizie numerycznej, która umoĪliwiła określenie wpływu para- metrów procesu na jego efektywność. 1. INTRODUCTION Pressure screening is the most efficient technique used for the mechanical separa- tion of various impurities from fibre suspensions during the paper recycling process. The removal of contaminants is carried out with a slotted screen cylinder (Fig. 1a) equipped with a rotor located inside which generates a tangential flow and pressure pulses (Fig. 1b) at the feed side of the semi-permeable surface. The fibres (1–3 mm long and 20–30 μm in diameter) pass fine slots (0.1–0.2 mm wide) and leave the ma- chine with the accepted flux (A in Fig. 1a). In the same time, larger contaminants are __________ * At present: Institute of Thermal Machinery, CzĊstochowa University of Technology, al. Armii Kra- jowej 21, 42-200 CzĊstochowa, Poland.