Rewetting and forming fabric structure

.................................................................................................. I SAMMANFATTNING ................................................................................... III LIST OF PAPERS ....................................................................................... V TABLE OF CONTENTS ............................................................................. VI 1 MOTIVATION ............................................................................................ 1 1.1 GLOBAL ENVIRONMENTAL ISSUES ............................................................ 1 1.2 THE INTERNATIONAL PULP AND PAPER INDUSTRY .................................... 1 1.3 THE SWEDISH PULP AND PAPER INDUSTRY ............................................. 2 2 THE PAPER MACHINE ............................................................................. 3 2.1 THE PAPER MACHINE .............................................................................. 3 2.2 RAW MATERIALS FOR PAPER PRODUCTION ............................................... 3 2.3 THE HEADBOX ....................................................................................... 4 2.4 THE FORMING SECTION .......................................................................... 5 2.4.1 Gravitational dewatering .............................................................. 5 2.4.2 Forming fabrics ............................................................................ 5 2.4.3 Foils .............................................................................................. 7 2.4.4 Vacuum dewatering ..................................................................... 7 2.4.5 Rewetting in the forming section .................................................. 9 2.4.6 Numerical models of flow through sheet and fabric ................... 12 2.4.7 Energy saving measures in the forming section ........................ 12 2.5 THE PRESS SECTION ............................................................................ 12 2.6 THE DRYING SECTION ........................................................................... 13 3 OBJECTIVES .......................................................................................... 14 4 MATERIALS AND METHODS ................................................................ 15 4.1 PILOT STUDY OF REWETTING AFTER HIGH VACUUM SUCTION .................... 15 4.1.1 Forming fabric ............................................................................ 15 4.1.2 Raw Materials ............................................................................ 15 4.1.3 Experimental set-up ................................................................... 15 4.2 LABORATORY-SCALE VACUUM DEWATERING ........................................... 19 4.2.1 Forming fabrics .......................................................................... 19 4.2.2 Raw materials ............................................................................ 20 4.2.3 Experimental set-up ................................................................... 21 4.2.4 Calculations ................................................................................ 22 4.2.5 Measurement uncertainty ........................................................... 22 4.3 NUMERICAL MODELS ............................................................................ 23