Totally updated version

Transcription

1 Papermaking Science and Technology a book series covering the latest technology and future trends Book 8 Papermaking Part 1, Stock Preparation and Wet End Second Edition Totally updated version Book editor Hannu Paulapuro, D. Sc. (Tech.), Professor, Department of Forest Products Technology, Paper Technology, Helsinki University of Technology Publisher Finnish Paper Engineers Association/Paperi ja Puu Oy Paperi ja Puu Oy

2 Table of Contents 1 Mill operations in the production of main paper and board grades an overview History of papermaking Slushing and defibration of pulp in the paper mill Refining of chemical pulp fibres Stock and water systems of the paper machine Web forming Air Forming Forming fabrics Wet pressing Press fabrics Paper machine rolls Vacuum systems Vacuum pumps Conversion factors Index

3 CHAPTER 1 Mill operations in the production of main paper and board grades an overview 1 Introduction Paper mill structure Mill Production lines Process and paper machine area Process Paper machine area Operating performance Various technical concepts Newsprint paper mill SC and LWC paper mill Fine paper mill Linerboard mill Board mill Tissue mill Mill organisation Trends...58 References

4 CHAPTER 2 History of papermaking 1 Pre-paper era Early writing surfaces Papyrus Parchment Other paper-type materials Entering the paper age China, the birthplace of paper Art of papermaking moving westward First use of paper in Europe First paper mills in Europe First paper mills in America Hand papermaking Main principles Raw materials Pretreatment of fibres Sheet forming and drying of paper Watermarks in hand-made paper Development of machines for papermaking The pioneer Nicolas-Louis Robert Development of the fourdrinier paper machine Development of the cylinder-mould machine Development of other paper machine types Breakthrough of machine-made paper Milestones in paper machine development Technical development - but a faster decaying product...75 References...76 For further reading

5 Chapter 3 Slushing and defibration of pulp in the paper mill 1 Bale handling Slushing Targets of slushing Pulpers Horizontal pulpers Vertical pulpers Pulper rotor Slushing system Instrumentation and control Pulper operating characteristics and effect on pulp properties Pulper operation mode Slushing energy Slushing consistency Slushing temperature and water quality Wet storage Defibration (defibering, deflaking, or disintegration) Targets of deflaking Type of deflakers Operating characteristics and effect on pulp properties Evaluation of the slushing and deflaking result Visual evaluation Optical and other sheet quality measurements Screening Stock Quality Degree (Metso) Energy Optimization Test (Fibre Technology Association)...90 References

6 Chapter 4 Refining of chemical pulp fibres 1 Introduction Fibre structural changes Internal fibrillation of fibre cell wall Changes in fibre curl; fibre straightening Fibre shortening External fibrillation and formation of fines Release of organic substances Historical development of refining Evolution of the Hollander beater The important role of the beaterman Evolution of disc and conical refiner Fibre-water suspension in low-consistency refining Orientation and state of fibres between refiner bars Fibrage Floc refining hypothesis Suspension flowing through the refining zone Primary flow in grooves and reverse flow Why are grooves needed? Modern low-consistency refiners Conical Refiner Disc refiner Cylindrical refiner Modern laboratory refiner Control and characterization of a low-consistency refiner Specific edge load and specific energy Number of impacts and severity of impacts

7 Refining of chemical pulp fibres 6.3 Characterisation of pulp refiners by C-factor Specific surface load Other approaches to characterise low-consistency refining Refining as part of the stock approach system High-consistency refining Potential of high-consistency refining in treating deinked pulps Effect of high-consistency treatments on fibre structure of deinked pulps Operation of low-consistency refiners Effect of pulp consistency ph and electrolyte content of pulp Chemical additives in refining Basic effect of intensity and specific energy on fibres Refiner filling materials and production technology Energy consumption in low-consistency refining Application of enzymes prior to refining Summary References

8 CHAPTER 5 Stock and water systems of the paper machine 1 Definitions Design principles Elements and operations System stability Grade changes Pressure variations and pulsation Stock consistency variations Headbox approach flow stability Stock and water balance Multi-ply and multiple-layer systems System cleanliness Simulation tools Stock flow operations Stock blending Stock dosage Stock dilution Principle Mixing Machine stock dilution Headbox dilution system Medium- and high-consistency stock dilution Cleaning and screening Hydro-cyclone cleaning Screening Deaeration Air in stock and water Effect of air on papermaking Sources of air Chemical deaeration Deaeration tanks Deaeration by other equipment Chemical conditioning Wet end chemistry

9 Stock and water systems of the paper machine Dosage points Dosing Measurements Stock transport Piping Pumping Stock chests Vertical chests Storage silos Agitators Retention times Broke system Introduction Broke system requirements Broke handling Transport and auxiliary equipment Pulpers Slushed broke-handling system Broke dosage Coated broke systems Fibre recovery and water clarification Filtration Disc filter Sweetener Other filters Flotation Classification Sedimentation Mill water systems Paper mill water household Fresh water use Dissolved and detrimental substances Accumulation mechanisms Vertically integrated mills Horizontally integrated mills Advanced water purification techniques Membrane filtration Evaporation Biological in-process treatment Novel approaches and possible future References

10 Chapter 6 Web forming 1 Grammage variability Power spectrum Fibre flocculation Sediment concentration Network generation Crowding factor Network strength Floc stretching Flocculation measurements Formation Optical methods Beta ray methods Formation characteristics Formation of random sheets Dewatering effects on formation Medium-scale grammage variations Headboxes Cross-direction distribution Air-cushion headboxes Hydraulic headboxes Turbulence generator effects Headbox nozzle Fibre orientation anisotropy Jet angle and velocity CD grammage profile Dilution control

11 Web forming 2.7 Multilayer headboxes High-concentration headboxes Wire sections Fibre deposition Forming fabrics Dewatering resistance Fourdrinier forming Table rolls Foil elements Dry suction boxes and couch roll Structure modification Twin-wire forming Roll forming Blade forming Hybrid forming Roll-blade forming New STFI Former Multi-ply/multilayer forming Separate forming Simultaneous forming Forming and paper strength References

12 Chapter 7 Air Forming 1 Introduction Furnish composition Fibres Binders Additives Process Typical layout of a modern air-laid process Kroyer and St. Anne's process Air-laid forming heads Sifting systems Kroyer design (now M&J Fibretech) Dan-Web design Honshu design Direct laying design (VNIIB) Features of air-laid forming Degree of pulp disintegration Aerodynamics of air-fibre flow Fibre concentration C f Effect of fibre charging and electrostatic force Strength of air-laid network Bonding of dry air-laid web Future development of air-laid process References

13 Chapter 8 Forming fabrics 1 Function of forming fabric Weave structure Materials Manufacturing Classification of forming fabrics Single layer SL Double layer DL Triple weft TW Triple layer TL Self-support binding SSB SSB forming fabrics Properties of forming fabrics having an influence on the papermaking process Dewatering Retention Sheet structure Stability Elasticity Stiffness Diagonal stability Tension profile Wear resistance Clean running Wire marking Forming fabrics for different former types by paper grade Selection criteria Runnability features Paper quality features

14 Forming fabrics 5.2 Choosing a forming fabric Paper grade Former type Fourdrinier and hybrid-former bottom position Hybrid-former top position Gap former Multi-fabric formers Keeping forming fabrics clean Soiling of forming fabrics Soiling mechanisms Factors affecting soiling Origin of soiling substances Anti-soil fabrics Anti-soil yarns Anti-soiling treatments of fabrics Anti-soil chemicals Cleaning of forming fabrics Cleaning during machine run Cleaning during shut-down Fabric damage during cleaning Forming fabrics on paper machine Installation of forming fabric Start-up Follow-up Drainage measurement Controlling wear Bottom side wear Paper side wear Internal wear References

15 Chapter 9 Wet pressing 1 Introduction History and past developments Fundamentals of wet pressing Modeling of wet pressing Water removal from the fibre wall Wet pressing variables and their effects Types of variable Process variables Water removal Sheet quality Equipment parameters Nip types Roll parameters Felt parameters Press section configuration Runnability and web transfer Web transfer Open draw Closed transfer Elimination of the open draw Different types of press section Press sections for printing and writing papers Press sections for packaging and board grades Innovative pressing/drying techniques Condebelt process Impulse drying References

16 Chapter 10 Press fabrics 1 Press felts Function Raw materials Manufacturing of press felt Modern press felt structures Technical properties Basis weight Thickness Stiffness and tensile strength Compressibility Air permeability and flow resistance Surface uniformity The press felt as a part of the wet pressing process Sheet dewatering Sheet transfer Sheet quality Directions for use Installation and start-up Guiding Cleaning and Conditioning Practical press section monitoring Moisture profile meters Press felt permeability Monitoring of vibration Special applications Press felts for impulse drying Seamed felts

17 Press fabrics 3 Shoe press belts Background Shoe press belt construction Nonvented belt designs Vented belt designs Press felt and belt interaction Compound bending on closed end belts Closed loop belt life Closed transfer and transfer belts Introduction Sheet tension in the open draw Closed draw presses Sheet transfer from press to dryer section Closed draw transfer between the press section and the dryer section Transfer belt concepts Function of a transfer belt Impact on paper properties Transfer belt operation Transfer belt applications References

18 Chapter 11 Paper machine rolls 1 Introduction Lead rolls Lead roll dimensioning Lead roll construction materials Lead roll bearings and lubrication Lead roll covers Web spreading rolls Threaded roll Centre-supported roll Curved spreader roll Suction and forming rolls General Forming rolls Suction Rolls General Suction boxes of the suction roll Suction roll shell Deflection-compensated rolls Deflection of rolls Deflection compensation Crowning Deflection-compensated rolls Zone-controlled deflection-compensated rolls Dimensioning of deflection-compensated rolls Centre rolls General Granite roll Centre rolls replacing granite rolls Grooved and drilled press rolls Calender rolls Chilled cast-iron rolls Soft calender rolls

19 Chapter 12 Vacuum systems 1 Introduction to high-vacuum dewatering Economic basis Speed High-vacuum zone in the wire section and dewatering equipment used Flatboxes Couch roll Replacing couch roll Effect of process variables Paper and board grades Modelling of vacuum dewatering Optimisation of vacuum profiles Vacuum dewatering curves An empirical model for vacuum dewatering Effect of furnish type on dewatering equations Fine paper furnishes Newsprint furnishes SC and LWC paper furnishes Effect of grammage on dewatering curves Effect of temperature on dewatering Calculation of dewatering profile A case study Closing remarks References

20 Chapter 13 Vacuum pumps 1 Types Suction points and vacuum systems Vacuum piping Air flow velocities Piping Valves Water separators Seal pits for water separators Header pipes for liquid ring pumps Sealing water for liquid ring pumps Noise Vacuum pump noise levels Noise abatement Instrumentation Main measurements for vacuum control Vacuum level control Sealing water for liquid ring pumps Restriction of turbo blower air amount Electrical References