Book 9 Papermaking Part 2, Drying · Papermaking Science and Technology a book series covering the...
28
Papermaking Science and Technology a book series covering the latest technology and future trends Book 9 Second Edition Totally updated version Book editor Markku Karlsson, D.Sc. (Tech.), Senior Vice President, Technology, UPM Publisher Paper Engineers’ Association/Paperi ja Puu Oy Paperi ja Puu Oy Papermaking Part 2, Drying
Transcript of Book 9 Papermaking Part 2, Drying · Papermaking Science and Technology a book series covering the...
Papermaking Science and Technologya book seriescovering the latesttechnology andfuture trends
Book 9
Second Edition
Totally updated version
Book editorMarkku Karlsson, D.Sc. (Tech.), Senior Vice President, Technology, UPM
PublisherPaper Engineers’ Association/Paperi ja Puu Oy
Paperi ja Puu Oy
Papermaking Part 2, Drying
12
Table of Contents1 Introduction to paper drying and its principles ..................................................................13
2 Fundamentals of paper drying ............................................................................................39
3 Multicylinder dryer and drying concepts ............................................................................78
4 Air impingement drying ....................................................................................................126
5 Drying of tissue ..................................................................................................................162
6 Drying of paperboard and packaging grades ...................................................................211
7 Drying and paper quality ...................................................................................................236
8 Automation in paper drying ..............................................................................................296
9 Energy management ..........................................................................................................336
10 Steam and condensate systems .......................................................................................374
11 Drying section ventilation and heat recovery ...................................................................436
12 Web handling .....................................................................................................................484
13 Dryer fabrics ......................................................................................................................542
14 Drives .................................................................................................................................578
15 Future outlook ....................................................................................................................617
Conversion factors .............................................................................................................626
Index ...................................................................................................................................628
13
CHAPTER 1 Introduction to paper drying and its principles
Introduction1 ..........................................................................................................................14
Basic requirements for a modern drying section2 ...............................................................16
Tasks and requirements for the drying section2.1 .......................................................................16
Production speed2.2 ...................................................................................................................17
Production line efficiency2.3 .......................................................................................................18
Space efficiency2.4 .....................................................................................................................19
Paper quality2.5 ..........................................................................................................................19
Drying methods3 ....................................................................................................................19
Energy consumption in paper drying4 ..................................................................................21
Developments in paper machine drying technology5 ..........................................................23
From two-tier to single-tier drying section5.1 ..............................................................................23
Two-tier configuration5.1.1 ................................................................................................23
Single-tier configuration5.1.2 .............................................................................................23
Web handling and runnability5.1.3 .....................................................................................24
Dryer fabrics5.1.4 ..............................................................................................................24
Inside the drying cylinder5.1.5 ...........................................................................................25
Inside the hood5.1.6 ..........................................................................................................25
Alternative drying methods5.2 ....................................................................................................26
Air dryers5.2.1 ...................................................................................................................26
Infrared dryers5.2.2 ...........................................................................................................27
High-intensity processes5.2.3 ............................................................................................28
Impingement drying5.2.4 ...................................................................................................30
Steam drying5.2.5 .............................................................................................................31
Modern drying section design and future trends6 ...............................................................31
Conclusions and future outlook7 ..........................................................................................33
References ............................................................................................................................35
39
CHAPTER 2 Fundamentals of paper drying
Introduction1 ..........................................................................................................................40
Properties of moist air2 .........................................................................................................40
Moisture in air2.1 ........................................................................................................................40
Relative humidity of air2.1.1 ...............................................................................................41
Specific 2.2 enthalpy and specific heat of moist air ......................................................................41
The 2.3 i/x chart ..........................................................................................................................42
Basic definitions2.4 .....................................................................................................................46
Drying process – the 3 characteristic drying curve ..............................................................47
Evaporation from the web4 ...................................................................................................50
Vapour partial pressure4.1 ..........................................................................................................51
Sorption isotherm5 ................................................................................................................52
Hysteresis5.1 ..............................................................................................................................53
Heat of sorption5.2 .....................................................................................................................54
Boundary conditions6 for heat transfer ................................................................................56
Influence of evaporation on convective heat transfer7 .......................................................57
Changes in 8 web structure during drying ............................................................................59
Capillary flow of free water9 .................................................................................................63
Movement of 10 bound water ..................................................................................................65
Vapour flow11 ..........................................................................................................................66
Thermal conductivity12 of paper ............................................................................................69
Summary13 ..............................................................................................................................73
References ............................................................................................................................74
78
CHAPTER 3 Multicylinder dryer and drying concepts
Introduction1 ..........................................................................................................................80
Cylinder dryer configurations 1.1 ................................................................................................80
Double-felted configuration1.1.1 ........................................................................................80
Single-felted configuration1.1.2 .........................................................................................81
Basic design concepts for most common paper grades2 ....................................................82
Design concepts for different paper and board grades 2.1 ..........................................................82
Wood-containing printing papers (newsprint, LWC and SC)2.1.1 .........................................82
Woodfree papers2.1.2 ........................................................................................................83
Linerboard machines2.1.3 ..................................................................................................84
Basic requirements for cylinder drying with different paper grades2.2 ........................................85
Newsprint2.2.1 ..................................................................................................................85
Woodfree papers2.2.2 ........................................................................................................85
SC (supercalendered) and LWC (light weight coated) papers2.2.3 .......................................86
Liner and fluting2.2.4 .........................................................................................................86
Sack paper2.2.5 .................................................................................................................86
Use of energy in multicylinder drying concepts2.3 .......................................................................86
Drying section curl control2.4 .....................................................................................................88
Double-felted drying section2.4.1 ......................................................................................89
Single-felted drying section2.4.2 ........................................................................................89
Curl control with impingement drying2.4.3 .........................................................................90
Drying section components3 ................................................................................................91
Cylinders and vacuum rolls3.1 ....................................................................................................91
Fabric lead rolls3.2 .....................................................................................................................91
Drying section runnability3.3 .......................................................................................................91
Tail threading in cylinder drying section3.4 ..................................................................................93
Tail threading conditions in a cylinder drying section3.4.1 ..................................................94
Open draw between press and drying sections3.4.2 ..........................................................95
79
Multicylinder dryer and drying concepts
Closed draw3.4.3 between press and drying sections ........................................................95
Ropeless tail threading through drying section3.4.4 ...........................................................96
Threading through surface sizing unit with ropes3.4.5 .......................................................96
Heat transfer4 in cylinder drying ..........................................................................................98
Total heat transfer coefficient 4.1 ................................................................................................98
Periodic variation of dryer surface temperature4.2 ....................................................................101
Condensate behaviour in the cylinder4.3 ...................................................................................101
Dryer drive power4.3.1 ....................................................................................................102
Condensate oscillation4.3.2 .............................................................................................103
Condensate film thickness4.3.3 .......................................................................................104
Spoiler bars 4.4 ........................................................................................................................105
Condensate coefficient4.5 .........................................................................................................106
Dryer with smooth inner surface4.5.1 ..............................................................................106
Dryer with spoiler bars4.5.2 .............................................................................................108
Contact coefficient4.6 ...............................................................................................................108
Moisture content4.6.1 ......................................................................................................108
Fabric or web tension4.6.2 ...............................................................................................109
Cylinder and web smoothness4.6.3 ..................................................................................110
Number of fabric contact points4.6.4 ...............................................................................110
Air film between cylinder and web4.6.5 ............................................................................110
Influence of cylinder temperature4.6.6 .............................................................................111
Use of press roll to produce contact4.6.7 .........................................................................112
Drying rate of multicylinder drying section5 ......................................................................112
Dryer steam pressures5.1 .........................................................................................................115
Other factors influencing drying rate5.2 ....................................................................................116
Drying section 5.3 simulation .....................................................................................................117
Single-layer model5.3.1 ...................................................................................................117
Multilayer model5.3.2 ......................................................................................................119
Example of simulation application5.3.3 ............................................................................120
Future outlook and summary6 ............................................................................................121
References ..........................................................................................................................123
126
CHAPTER 4 Air impingement drying
I1 ntroduction........................................................................................................................128
Direct impingement1.1 .............................................................................................................129
Indirect impingement1.2 ...........................................................................................................129
Impingement heat transfer2 ................................................................................................130
Hydrodynamics of the impingement flow 2.1 ............................................................................131
Impingement flow – process description2.2 ..............................................................................131
Conventional empirical correlation2.3 for impingement heat transfer ........................................132
Influences of process parameters on impingement heat transfer3 ..................................134
Effect of evaporation on heat transfer3.1 ..................................................................................135
Effect of surface movement on heat transfer3.2 ........................................................................136
Effect of jet angle on heat transfer3.3 .......................................................................................136
Effect of through-flow on heat transfer 3.4 ................................................................................137
Effect of the cross-flow3.5 ........................................................................................................137
Effect of large temperature differences3.6 ................................................................................138
Experimental determination of convective heat transfer coefficient (CHTC)4 ..................138
Influence of thermal radiation on total heat transfer 4.1 ............................................................139
Empirical correlation for impingement heat transfer 4.2 ............................................................140
Modelling of the impingement heat transfer process4.3 ............................................................141
Impingement dryer design considerations5 .......................................................................141
Heat transfer coefficient5.1 .......................................................................................................142
Geometry optimization5.2 .........................................................................................................142
Drying parameters5.3 ...............................................................................................................143
Optimal air-system5.4 ...............................................................................................................144
Heat recovery system5.5 ..........................................................................................................144
Control system5.6 .....................................................................................................................144
Thermal expansions5.7 .............................................................................................................145
Energy consideration5.8 ...........................................................................................................145
127
Air impingement drying
Impingement drying applications6 .....................................................................................145
Impingement dryer with big vacuum roll 6.1 .............................................................................145
Impingement dryer with big vacuum rolls immediately after press section6.2 ...........................148
Impingement dryer on small vacuum rolls 6.3 ...........................................................................148
Impingement dryer on grooved rolls6.4 .....................................................................................149
Design concept for increasing production capacity6.4.1 ...................................................149
Design concept for beginning of drying section with grooved supporting rolls6.5 ......................152
Draw management with cylinder drying section6.5.1 .......................................................152
Technology 6.5.2 ..............................................................................................................153
Drying capacity6.5.3 ........................................................................................................154
Draw management 7 ...........................................................................................................154
Bulk8 saving potential with copy paper .............................................................................154
Sticking9 prevention with impingement drying ................................................................155
Summary10 ............................................................................................................................156
References ..........................................................................................................................157
Nomenclature ......................................................................................................................160
162
CHAPTER 5 Drying of tissue
Introduction1 ........................................................................................................................164
Yankee drying2 ....................................................................................................................164
Tissue drying process2.1 ..........................................................................................................164
Fundamentals of heat and mass transfer in tissue drying2.1.1 .........................................166
Sheet adhesion2.1.2 ........................................................................................................169
Dryer coating2.1.3 ...........................................................................................................170
Chemicals for controlling coating and sheet adhesion2.1.4 ..............................................171
Yankee doctors2.1.5 .........................................................................................................171
Web structure and properties2.1.6 ...................................................................................172
Yankee dryer design 2.2 ............................................................................................................173
General description2.2.1 ..................................................................................................173
Manufacturing and materials2.2.2 ....................................................................................174
Cylinder design2.2.3 ........................................................................................................174
Steel Yankee2.2.4 drying cylinders in tissue machines .....................................................178
Steam and condensate system for a tissue Yankee dryer2.3 .....................................................179
Design and functional description2.3.1 .............................................................................179
Safety considerations2.4 ...........................................................................................................181
Stress analysis2.4.1 .........................................................................................................181
Deformation analysis2.4.2 ................................................................................................182
Reconditioning of Yankee cylinders by thermal spraying2.5 .......................................................184
Yankee hood drying, ventilation and heat recovery3 .........................................................185
Yankee hood drying process3.1 .................................................................................................185
Yankee hood3.2 ........................................................................................................................185
Yankee hood types3.2.1 ...................................................................................................186
Design criteria3.2.2 ..........................................................................................................186
163
Drying of tissue
Yankee hood ventilation3.3 .......................................................................................................187
Yankee hood air systems3.3.1 ..........................................................................................187
Yankee hood air profiling 3.3.2 .........................................................................................189
Yankee hood air balancing systems3.3.3 ..........................................................................191
Tissue machine energy balance3.3.4 ...............................................................................191
Yankee hood retraction mechanism3.3.5 ..........................................................................192
Auxiliary equipment of Yankee hood3.3.6 .........................................................................192
Process air fans3.3.7 .......................................................................................................193
Air heating3.3.8 ...............................................................................................................194
Yankee section heat recovery3.4 ...............................................................................................194
Heat recovery from exhaust air3.4.1 ................................................................................194
Control systems3.5 ...................................................................................................................195
High-temperature hood3.6 ........................................................................................................196
Through-air drying of tissue (TAD)4 ...................................................................................197
Description of the through-air drying process4.1 .......................................................................198
Through-air drying vs. other drying methods4.2 ........................................................................199
Drying rates 4.2.1 ............................................................................................................199
Product properties4.2.2 ....................................................................................................200
Production costs4.2.3 ......................................................................................................201
Different machine configurations4.3 .........................................................................................201
Advantages of hybrid technologies in making high-quality tissue paper 5 ......................202
ATMOS tissue concept 5.1 ........................................................................................................202
Advantage NTT tissue making concept5.2 .................................................................................205
Summary6 ............................................................................................................................207
References ..........................................................................................................................209
211
CHAPTER 6 Drying of paperboard and packaging grades
Introduction1 ........................................................................................................................212
Containerboards2 ................................................................................................................213
Layout2.1 .................................................................................................................................213
Design criteria and drying rate2.2 .............................................................................................215
Effect on board quality2.3 .........................................................................................................216
Sack paper2.4 ..........................................................................................................................217
Other drying methods2.5 ..........................................................................................................218
Condebelt drying 2.5.1 .....................................................................................................218
High Efficiency Dryer2.5.2 ................................................................................................221
Cartonboards3 .....................................................................................................................223
Layout3.1 .................................................................................................................................223
Design criteria and drying rate3.2 .............................................................................................225
Effect on board quality3.3 .........................................................................................................227
Metal belt calender3.4 ..............................................................................................................227
Speciality papers and boards4 ............................................................................................229
Machine glazed drying for wrapping paper4.1 ...........................................................................229
Heat and mass transfer considerations in paper and paperboard 5
finishing and converting ....................................................................................................230
General5.1 ................................................................................................................................230
Corrugated board5.2 manufacture ............................................................................................230
Preheating, preconditioning and corrugating5.2.1 ............................................................231
Gluing5.2.2 ......................................................................................................................232
Preheater tower5.2.3 .......................................................................................................232
Double-facer5.2.4 ............................................................................................................232
Summary6 ............................................................................................................................233
References ..........................................................................................................................235
236
CHAPTER 7 Drying and paper quality
Introduction 1 .......................................................................................................................238
Drying of a single fibre 2 .....................................................................................................238
Fibre shrinkage and removal of water fractions 2.1 ...................................................................238
Inter-fibre bonding2.2 ...............................................................................................................240
Mechanical properties of fibres2.3 ............................................................................................241
Impacts of fibre morphology during drying 3 .....................................................................243
Plasticity and viscoelasticity of material3.1 ...............................................................................243
Fibre 3.2 softening .....................................................................................................................243
Hornification of cellulose fibres 3.3 ...........................................................................................245
Fibre sticking and adhesion to cylinder surface 3.4 ...................................................................246
Drying of a paper web 4 ......................................................................................................249
Different phases of paper drying4.1 ..........................................................................................250
Drying and web rheology4.2 .....................................................................................................251
Creep and tension relaxation4.3 ................................................................................................251
Paper shrinkage during drying5 .........................................................................................252
Definitions of drying stresses and deformations5.1 ...................................................................252
Paper deformation during drying5.2 ..........................................................................................253
In-plane shrinkage 5.3 ..............................................................................................................253
Development of mechanical properties of a web6 .............................................................255
Effects of machine-direction draw during drying6.1 ..................................................................257
Effects of cross-direction shrinkage during drying 6.2 ...............................................................258
Development of hydrogen bonding of the web during drying6.3 ................................................259
Web peeling from press roll 7 .............................................................................................261
Tension relaxation of the wet web 7.1 .......................................................................................263
Effects of drying temperature on paper quality8 ...............................................................265
Web drying in thickness direction9 ....................................................................................269
237
Drying and paper quality
Flatness deviations10 ............................................................................................................270
Challenges caused by efficiency improvement10.1 .....................................................................270
Curl10.2 ......................................................................................................................................271
One-sided drying10.2.1 .....................................................................................................272
Asymmetric moisture treatment10.2.2 ...............................................................................273
Curl and its control 10.2.3 ..................................................................................................274
Cockling 10.3 ..............................................................................................................................275
Streakiness and waviness in machine direction 10.3.1 .......................................................276
Lumpiness 10.3.2 ..............................................................................................................280
Drying-induced profiles of a web 11 ....................................................................................280
Shrinkage profile of a web11.1 ...................................................................................................281
Tension profile of a web 11.2 ......................................................................................................283
Drying of paper coatings and surface size12 .......................................................................285
Drying of precoat and surface size12.1 .......................................................................................285
Drying strategy and quality in pigment drying12.2 ......................................................................285
Moisture changes in printing and end use 13 ......................................................................287
Heatset waviness 13.1 ................................................................................................................287
Stack waviness13.2 ....................................................................................................................288
Development trends 14 ..........................................................................................................289
References ..........................................................................................................................290
296
CHAPTER 8 Automation in paper drying
Introduction1 ........................................................................................................................298
Control theory – opportunities and limitations1.1 ......................................................................299
Water to be removed in papermaking1.2 ...................................................................................302
Cylinder drying and steam system1.3 .......................................................................................302
Disturbances to be eliminated by automation1.4 .......................................................................302
Paper quality measurements and problems in paper scanning1.5 .............................................303
MD and CD controls1.6 .............................................................................................................303
Grade changes1.7 .....................................................................................................................304
Cylinder drying and steam system2 ...................................................................................304
Cylinder drying2.1 .....................................................................................................................304
Steam and condensate system2.2 ............................................................................................305
Capability to control moisture level in paper2.3 .........................................................................307
Paper quality measurements3 ............................................................................................308
Scanning measurement3.1 .......................................................................................................308
Control challenges related to measurement principle3.2 ...........................................................309
Steam box4 ..........................................................................................................................310
Product and its applications4.1 .................................................................................................310
Moisturising system5 ..........................................................................................................312
Product and its applications5.1 .................................................................................................312
MD controls 6 .......................................................................................................................314
Products and applications6.1 ....................................................................................................314
Dryer control concept6.2 ...........................................................................................................316
Stock preparation and wet end controls6.3 ...............................................................................318
MPC based control of paper moisture6.4 ...................................................................................319
Impingement drying7 ..........................................................................................................319
Hood and heat recovery management8 ..............................................................................321
297
Automation in paper drying
CD controls9 .........................................................................................................................323
Products, technologies and applications9.1 ...............................................................................323
CD moisture control9.2 .............................................................................................................326
MPC technology for CD moisture control9.3 ..............................................................................328
Grade change10 .....................................................................................................................328
Development opportunities11 ...............................................................................................331
References ..........................................................................................................................334
336
CHAPTER 9 Energy management
Energy generation and use in integrated pulp and paper mills1 .......................................338
Introduction1.1 .........................................................................................................................338
Energy use at integrated mills1.2 ..............................................................................................340
Energy use in unit processes 1.2.1 ...................................................................................340
Energy quality 1.2.2 .........................................................................................................341
Influence of paper drying method on energy use1.2.3 ......................................................341
Energy production at integrated mills 1.3 ..................................................................................342
Energy balances1.3.1 .......................................................................................................342
Energy system design 1.3.2 .............................................................................................344
Benefits of integration 1.3.3 .............................................................................................344
Trends in energy use and their consequences1.3.4 ..........................................................347
Fuel quality improvement by drying1.3.5 ..........................................................................348
Energy efficiency1.4 ................................................................................................................349
Energy efficiency indicators 1.4.1 .....................................................................................349
Conceptual challenges related to 1.4.2 energy efficiency ..................................................350
Energy efficiency1.4.3 management ................................................................................351
Process systems analysis methods1.4.4 ..........................................................................353
Total efficiency aspects 1.4.5 ...........................................................................................355
Energy management at paper machine level 2 ..................................................................356
Drying section as part of an integrated mill2.1 ..........................................................................356
Benchmarking papermaking energy consumption 2.2 ...............................................................357
PM line energy consumption allocation 2.3 ...............................................................................359
Drying section energy consumption and related factors2.4 .......................................................361
Electricity consumption2.4.1 ............................................................................................362
Heat consumption2.4.2 ....................................................................................................363
Energy efficiency of different drying methods2.4.3 ...........................................................366
337
Energy management
Energy efficiency analysis based on automation system data2.4.4 ...................................367
Energy efficiency monitoring2.4.5 ....................................................................................367
Example of energy efficiency program2.4.6 ......................................................................368
Future development of energy efficiency in papermaking2.5 .....................................................369
References ..........................................................................................................................371
374
CHAPTER 10 Steam and condensate systems
Introduction 1 .......................................................................................................................376
Steam requirements2 ..........................................................................................................378
Steam pressure2.1 ...................................................................................................................379
Steam temperature2.2 ..............................................................................................................379
Equipment3 ..........................................................................................................................380
Condensate tanks3.1 ................................................................................................................381
Condenser3.2 ...........................................................................................................................382
Condensate pumps3.3 ..............................................................................................................382
Vacuum pumps3.4 ....................................................................................................................383
Design criteria of steam drying systems4 ..........................................................................383
General4.1 ................................................................................................................................383
Design principles by cylinder dryer configuration 4.2 ................................................................383
Design principles by grade 4.3 ..................................................................................................385
Dryers condensing and condensate removal5 ...................................................................386
Steam and condensate connections5.1 .....................................................................................388
Condensate removal equipment5.2 ...........................................................................................389
General5.2.1 ....................................................................................................................389
Stationary siphon 5.2.2 ....................................................................................................391
Rotary siphon5.2.3 ..........................................................................................................397
Controlling pressure and 5.3 differential pressure ......................................................................402
General5.3.1 ....................................................................................................................402
Differential pressure control5.3.2 .....................................................................................403
Flow control5.3.3 .............................................................................................................404
Steam and condensate systems6 .......................................................................................404
Cascade system6.1 ...................................................................................................................405
Operating and design principles6.1.1 ...............................................................................405
Division of steam sections 6.1.2 .......................................................................................407
375
Steam and condensate systems
Applications6.1.3 .............................................................................................................409
Advantages and disadvantages of 6.1.4 cascade systems .................................................412
Simulation6.1.5 ................................................................................................................412
Thermocompressor systems6.2 ...............................................................................................413
Construction and operation of a thermocompressor6.2.1 ..................................................413
Performance6.2.2 ............................................................................................................415
Thermocompressor pressure control system6.2.3 ............................................................418
Thermocompressor pressure control system with differential control valve6.2.4 ...............419
Dryer differential control using the thermocompressor spindle6.2.5 .................................419
Advantages and disadvantages of 6.2.6 thermocompressor systems ................................421
Cascade thermocompressor system6.3 .....................................................................................421
Thermocompressor system6.4 for Yankee dryer ........................................................................423
Vacuum control and air venting6.5 ............................................................................................424
Heating air with steam7 ......................................................................................................426
General7.1 ................................................................................................................................426
Applications7.2 .........................................................................................................................427
Heating water with steam 8 ................................................................................................429
General 8.1 ...............................................................................................................................429
Applications8.2 .........................................................................................................................430
Condensate recovery and return9 .......................................................................................430
Development trends10 ...........................................................................................................432
References .........................................................................................................................433
Appendix .............................................................................................................................434
436
CHAPTER 11 Drying section ventilation and heat recovery
Introduction1 ........................................................................................................................438
Drying section air systems2 ................................................................................................439
Design criteria2.1 .....................................................................................................................439
Drying section hood2.2 .............................................................................................................440
Hood types2.2.1 ...............................................................................................................440
Exhaust air humidity2.2.2 ................................................................................................441
Dew point2.2.3 ................................................................................................................442
Pressure levels and 2.2.4 air balance ................................................................................442
Air handling in the closed hood2.2.5 ................................................................................444
General aspects of hood design2.2.6 ................................................................................445
Drying section ventilation2.3 .....................................................................................................446
Pocket ventilation2.3.1 concepts ......................................................................................447
Pocket ventilation for different paper and board grades2.3.2 ............................................448
Ventilators2.3.3 for single-felting .....................................................................................449
2.3.4 Pocket ventilation parameters .................................................................................450
Profiling2.3.5 by means of ventilation ...............................................................................451
Supply 2.3.6 air distribution ..............................................................................................451
Integration of drying section air systems and sheet 2.4 runnability systems ...............................452
Design criteria related to sheet runnability systems2.4.1 ..................................................453
Drying section heat recovery3 ............................................................................................454
Drying section 3.1 energy balance .............................................................................................454
General aspects of drying section energy use and management3.2 ..........................................459
Process parameters3.2.1 .................................................................................................459
Control systems3.2.2 .......................................................................................................461
Heat recovery systems3.2.3 .............................................................................................461
Process improvements3.2.4 .............................................................................................462
Application of new technologies3.2.5 ...............................................................................462
437
Drying section ventilation and heat recovery
General basis for 3.3 heat recovery system design .....................................................................463
Energy prices3.4 .......................................................................................................................464
Continuity3.5 ............................................................................................................................465
Heating requirements3.6 ...........................................................................................................466
Basic types of 3.7 heat exchanger .............................................................................................467
Air/air heat exchangers3.7.1 ............................................................................................467
Air/water heat exchangers3.7.2 .......................................................................................468
Scrubbers3.7.3 ................................................................................................................469
Air coils3.7.4 ....................................................................................................................469
Different types of 3.8 heat recovery system ...............................................................................470
Earlier types of heat recovery system3.8.1 .......................................................................470
Contemporary heat recovery system designs3.8.2 ...........................................................471
High-temperature heat recovery3.8.3 ...............................................................................472
Heat recovery in 3.8.4 air dryers for coating ......................................................................472
Heat recovery in 3.8.5 pulp dryers ....................................................................................473
Other applications3.8.6 ....................................................................................................473
Sizing and optimisation of heat recovery systems3.8.7 ....................................................474
Design criteria for heat recovery equipment3.8.8 .............................................................475
Environmental aspects related to drying section ventilation4 ..........................................475
Sound attenuation4.1 ................................................................................................................475
Absorptive (resistive) 4.1.1 silencers .................................................................................477
Reactive 4.1.2 silencers ....................................................................................................477
Plume4.2 remediation ...............................................................................................................478
Process 5 ventilation control ...............................................................................................479
Basic control system5.1 ............................................................................................................479
Energy management5.2 systems ..............................................................................................480
Development trends and future concepts in paper machine ventilation6 ........................481
References ..........................................................................................................................483
484
CHAPTER 12 Web handling
I1 ntroduction........................................................................................................................486
Dynamics of a moving web2 ...............................................................................................487
Forces influencing a web2.1 .....................................................................................................488
External forces2.1.1 .........................................................................................................488
Acceleration forces in out-of-plane direction of the web2.1.2 ...........................................490
Thread-line model2.2 ................................................................................................................491
Longitudinal wave equation2.2.1 ......................................................................................491
Out-of-plane wave equation2.2.2 .....................................................................................492
Material properties of a web3 .............................................................................................493
Rheology of a web3.1 ...............................................................................................................493
Models of web rheology3.2 .......................................................................................................500
Uni-axial models3.2.1 ......................................................................................................500
Multi-axial models3.2.2 ....................................................................................................503
Aerodynamics of moving webs4 .........................................................................................504
Boundary layers on a flat plate4.1 .............................................................................................504
Pressure development in pockets4.2 .........................................................................................505
Web flutter and aerodynamic added mass4.3 ............................................................................507
Effect of geometry on web flutter4.3.1 .............................................................................507
Air flows and runnability systems in drying section5 ........................................................508
Paper machine speed development 5.1 .....................................................................................508
Air flow-induced runnability problems5.2 ..................................................................................509
Double-felted drying sections5.3 ...............................................................................................510
Single-felted drying sections5.4 ................................................................................................510
Single felting with small-diameter vacuum roll5.4.1 .........................................................511
Single felting with grooved larger-diameter vacuum roll5.4.2 ...........................................512
Drying section geometry with perforated bottom rolls 5.4.3 ..............................................515
Principle for app5.5 lication of runnability systems .....................................................................516
485
Web handling
Fluid flow analysis and computational fluid dynamics6 ...................................................516
Web tension7 .......................................................................................................................519
Strain behaviour of a moving web7.1 ........................................................................................519
Unsupported web7.2 .................................................................................................................520
Tension behaviour of steady-state web7.2.1 ....................................................................520
Tension behaviour of unsupported continuous web7.2.2 ...................................................521
Tension behaviour of a supported web7.3 .................................................................................525
Effects of fabrics on strain behaviour7.3.1 ........................................................................525
Two-dimensional planar strain and tension fields8 ...........................................................526
Planar stationary elastic and visco-elastic web8.1 ....................................................................526
Effects of the moving web8.2 ....................................................................................................527
Internal strains and shrinkages8.3 ............................................................................................528
Tension profile8.4 .....................................................................................................................529
Future trends in web handling9 ..........................................................................................532
References ..........................................................................................................................533
Nomenclature ......................................................................................................................539
542
CHAPTER 13 Dryer fabrics
Introduction1 ........................................................................................................................544
Role of dryer fabrics in paper drying2 ................................................................................544
Fabric as part of the drying process2.1 .....................................................................................546
Heat transfer2.1.1 ............................................................................................................546
Evaporation2.1.2 ..............................................................................................................548
Ventilation2.1.3 ................................................................................................................549
Air permeability2.1.4 ........................................................................................................551
Web support and runnability2.2 .................................................................................................551
Effects of fabrics in air transport2.2.1 ..............................................................................553
Fabric-to-web contact and CD web shrinkage control2.2.2 ..............................................554
Effects of dryer fabrics on web strain behaviour and speed differences 2.2.3 ...................557
Dryer fabric marking2.2.4 ................................................................................................559
Dryer fabric structures3 ......................................................................................................560
Raw materials3.1 ......................................................................................................................560
Traditional and modern structures3.2 ........................................................................................563
Seams3.3 .................................................................................................................................564
Dryer fabric dimensions3.4 .......................................................................................................565
Selection of dryer fabric type4 ............................................................................................566
Dryer fabrics for impingement drying units4.1 ..........................................................................567
Operative use5 .....................................................................................................................568
Installation5.1 ...........................................................................................................................568
Guiding5.2 ................................................................................................................................568
Cleaning5.3 ..............................................................................................................................569
Consequences of contamination5.3.1 ...............................................................................569
Types of contaminant5.3.2 ...............................................................................................569
Fabric application and cleaning recommendations5.3.3 ...................................................570
543
Dryer fabrics
Clothing follow-up service6 ................................................................................................572
Fabric inspections6.1 ................................................................................................................573
Troubleshooting6.2 ...................................................................................................................574
Optimising tools6.3 ...................................................................................................................574
Future dryer fabrics7 ...........................................................................................................575
References ..........................................................................................................................576
578
CHAPTER 14 Drives
Introduction1 ........................................................................................................................580
Dimensioning and selection of components2 ....................................................................580
General principles2.1 ................................................................................................................580
Dimensioning of mechanical drives2.2 ......................................................................................581
Criteria for selecting separate transmissions2.2.1 ............................................................582
Criteria for selecting couplings and universal shafts2.2.2 .................................................583
Dimensioning of electrical drives2.3 ..........................................................................................586
Mechanical drives3 ..............................................................................................................587
Main shaft drives3.1 .................................................................................................................587
Belt drives3.1.1 ................................................................................................................588
Differential drives3.1.2 .....................................................................................................588
Sectional drives3.2 ...................................................................................................................589
Separate transmissions3.2.1 ............................................................................................591
Roll gearbox3.2.2 .............................................................................................................593
Drying section3.2.3 drives ................................................................................................595
Electrical drives4 .................................................................................................................597
History4.1 .................................................................................................................................597
Variable-speed drive4.2 ............................................................................................................597
DC drive4.2.1 s .................................................................................................................597
AC drive4.2.2 s with asynchronous induction motors .........................................................598
AC drives with synchronous 4.2.3 permanent magnet motors ...........................................600
Sectional drive system 4.3 ........................................................................................................600
AC or DC drive with a speed reduction gear4.3.1 ..............................................................601
Direct drive without speed reduction gear4.3.2 ................................................................602
Machine integrated motor4.3.3 ........................................................................................603
Energy efficiency of drive system4.4 .........................................................................................603
579
Drives
Controls4.5 ...............................................................................................................................604
Different running modes4.5.1 ...........................................................................................605
Different control modes4.5.2 ............................................................................................605
Control modes in a paper machine4.5.3 ...........................................................................606
Speed reference chain4.5.4 .............................................................................................607
Control performance4.6 ............................................................................................................609
Configuration4.6.1 ...........................................................................................................609
Control accuracy and resolution4.6.2 ...............................................................................609
Static accuracy4.6.3 ........................................................................................................609
Dynamic accuracy4.6.4 ....................................................................................................610
Paper transport considerations4.6.5 .................................................................................610
Controllers4.6.6 ...............................................................................................................611
Operator interfaces4.7 ..............................................................................................................613
Local control devices4.7.1 ................................................................................................613
Supervisory systems4.7.2 ................................................................................................614
Maintenance tools4.8 ................................................................................................................614
Future of drives5 ..................................................................................................................615
References ..........................................................................................................................616
617
CHAPTER 15 Future outlook
Drying concepts1 .................................................................................................................618
Energy management 2 .........................................................................................................620
Ventilation, heat recovery and runnability systems 3 ........................................................620
Paper and board grades4 ....................................................................................................621
Other drying section systems5 ...........................................................................................622
Modelling and simulation of complicated interactions in paper drying6 .........................623
Conclusion7 ..........................................................................................................................624
References ..........................................................................................................................625
