Chemical Pulping

"Chemical Pulping"Edited by Johan Gullichsen

AndCarl-Johan Fogelholm

Item Number: 0202FIN06ISBN: 952-5216-06-32 volumes, Volume A - 693 pages, Volume B - 497 pages

Volume AChapter 1 - Introduction

1 Wood fibers.........................................................................................................................132 Pulping ................................................................................................................................132.1 Washing, screening, and bleaching .....................................................................................142.2 Recovery of chemicals .........................................................................................................15

Chapter 2 - Fiber line operations

1 Principles of wood chip delignification ...........................................................................191.1 Properties of wood chips......................................................................................................19

1.1.1 Structure of wood.....................................................................................................191.1.2 Chemical composition of wood................................................................................23

1.2 Chemical pulping methods...................................................................................................281.3 Principles of chemical pulping reactions ..............................................................................321.4 Alkaline processes ...............................................................................................................38

1.4.1 The kraft process .....................................................................................................381.4.2 Modified kraft processes..........................................................................................521.4.3 Principles of industrial cooking ................................................................................601.4.4 Heat and material balances in kraft pulping ............................................................73

1.5 Acid processes.....................................................................................................................861.5.1 Sulfite pulping ..........................................................................................................86

1.6 Process variables in sulfite cooking .....................................................................................961.6.1 Principles of industrial..............................................................................................981.6.2 Process variables and fiber quality........................................................................101

1.7 Semichemical and chemimechanical pulping methods .....................................................1021.7.1 Neutral semichemical pulping................................................................................1031.7.2 NSSC pulping principle..........................................................................................1031.7.3 NSSC pulping and its process variables ...............................................................104

2 Pulp washing ....................................................................................................................1072.1 Principles of washing .........................................................................................................108

2.1.1 Terminology ...........................................................................................................1082.1.2 Principles of washing .............................................................................................1082.1.3 Washers.................................................................................................................109

3 Screening and cleaning of pulp......................................................................................1173.1 Typical solid impurities .......................................................................................................1183.2 General principles of screening and cleaning ....................................................................122

3.2.1 Equipment and flow sheet symbols .......................................................................1223.2.2 Principles of screening...........................................................................................124

3.3 Screening operations .........................................................................................................1253.3.1 Knotting..................................................................................................................1253.3.2 Brownstock screening............................................................................................1263.3.3 Flow balance of brown stock screening.................................................................1273.3.4 Typical screening equipment .................................................................................1293.3.5 Screening layout considerations............................................................................1313.3.6 Screen plates.........................................................................................................131



3.3.7 Medium-consistency screening .............................................................................1323.3.8 Principles of cleaning.............................................................................................1333.3.9 Cleaner applications ..............................................................................................1343.3.10 Hydro-cyclone systems..........................................................................................135

4 Oxygen delignification.....................................................................................................1374.1 Short history .......................................................................................................................1384.2 The basic process ..............................................................................................................1384.3 The basic chemistry of oxygen delignification....................................................................139

4.3.1 Selectivity...............................................................................................................1404.3.2 Reaction rates and mass transfer..........................................................................1414.3.3 Chemical consumption and reaction products.......................................................141

4.4 Processes and equipment..................................................................................................1414.4.1 Process variables ..................................................................................................1444.4.2 Placing oxygen delignification in a pulping line .....................................................1444.4.3 Quality of oxygen delignification ............................................................................146

5 Bleaching of pulp .............................................................................................................1465.1 Optical properties of pulp ...................................................................................................146

5.1.1 Stability of brightness.............................................................................................1505.2 Bleaching chemicals and reaction principles .....................................................................1505.3 Bleaching sequences .........................................................................................................1565.4 Process variables and equipment in bleaching stages......................................................158

5.4.1 The gas-liquid-fiber system....................................................................................1585.4.2 Chlorination............................................................................................................1585.4.3 Alkaline extraction..................................................................................................1765.4.4 Chlorine dioxide bleaching.....................................................................................1805.4.5 The standard chlorine and chlorine dioxide bleaching sequence..........................1885.4.6 Hypochlorite and hypochlorous acid bleaching .....................................................1905.4.7 Ozone delignification .............................................................................................1945.4.8 Hydrogen peroxide bleaching................................................................................202

5.5 Displacement bleaching .....................................................................................................2135.5.1 Process applications of displacement bleaching...................................................216

6 Cooking, washing, screening, and bleaching process units ......................................2197 Drying of pulp...................................................................................................................2257.1 Sheet dryers .......................................................................................................................2267.2 Flash drying........................................................................................................................2287.3 Quality aspects of drying....................................................................................................2287.4 Heat and mass transfer in pulp drying ...............................................................................229

References.........................................................................................................................231

Chapter 3 - Chemical engineering principles of fiber line operations

1 Physics and fluid mechanics..........................................................................................2451.1 Cooking of chips.................................................................................................................245

1.1.1 Anatomy of wood chips..........................................................................................2451.1.2 Compressibility of chip columns and their resistance to liquid flow.......................255

1.2 Fiber phase operations ......................................................................................................2601.2.1 Fiber rheology........................................................................................................2601.2.2 Pumping of fiber suspensions................................................................................2691.2.3 Mixing.....................................................................................................................2751.2.4 Reactors and tanks................................................................................................2771.2.5 Screening and cleaning .........................................................................................2801.2.6 Filtration, displacement, and pressing ...................................................................287



2 Reaction kinetics and mass transfer .............................................................................2912.1 Reaction kinetics in kraft cooking.......................................................................................291

2.1.1 Kinetics of lignin reactions .....................................................................................2912.1.2 Kinetics of carbohydrate reactions ........................................................................294

2.2 Mass transfer in kraft cooking ............................................................................................2952.2.1 Steaming................................................................................................................2952.2.2 Penetration.............................................................................................................2972.2.3 Diffusion .................................................................................................................2982.2.4 Sorption..................................................................................................................3012.2.5 Applications and examples ....................................................................................301

2.3 Mass transfer and kinetics in fiber phase processes .........................................................3042.3.1 Mass transfer in bleaching.....................................................................................3042.3.2 Reaction kinetics in bleaching ...............................................................................308

2.4 Mass transfer in washing ...................................................................................................3132.4.1 Displacement efficiency in washing.......................................................................3142.4.2 Diffusion and sorption phenomena in washing......................................................3162.4.3 Comparison of efficiency of different washing systems.........................................3202.4.4 Fractional washing.................................................................................................323

3 Heat transfer .....................................................................................................................3233.1 Heat capacity and heat balances of solid-liquid-gas mixtures ...........................................3233.2 Rate of heat transfer ..........................................................................................................325

References.........................................................................................................................326

Chapter 4 - Wood handling applications

1 Measuring, storing, and pretreatment of roundwood ..................................................3311.1 Measuring incoming wood raw material.............................................................................332

1.1.1 Wood weighing ......................................................................................................3321.1.2 Scanning image scaling.........................................................................................335

1.2 Wood storage arrangements at the mill site ......................................................................3371.2.1 Storage area ..........................................................................................................3381.2.2 Storage time...........................................................................................................3381.2.3 Wood unloading.....................................................................................................338

1.3 Deicing, cutting, and feeding to debarking.........................................................................3421.3.1 Receiving conveyor ...............................................................................................3431.3.2 Deicing ...................................................................................................................3441.3.3 Receiving deck ......................................................................................................3461.3.4 Slasher deck ..........................................................................................................3471.3.5 Sorting....................................................................................................................3471.3.6 Waste handling ......................................................................................................3481.3.7 Feed into debarking ...............................................................................................348

2 Debarking..........................................................................................................................3512.1 Tumble debarking ..............................................................................................................3562.2 Parallel debarking ..............................................................................................................3622.3 Ring debarking ...................................................................................................................3632.4 King debarking ...................................................................................................................3662.5 Hydraulic debarking ...........................................................................................................3672.6 Small diameter wood debarking.........................................................................................3672.7 Chain flail debarking...........................................................................................................3683 Chipping............................................................................................................................3693.1 Horizontally fed chippers....................................................................................................3793.2 Gravity fed chippers ...........................................................................................................380



3.3 Drum chippers....................................................................................................................3823.4 Chipper feeding..................................................................................................................3834 Chip screening .................................................................................................................3864.1 Coarse screen....................................................................................................................3964.2 Gyrating screens ................................................................................................................3964.3 Disc screens.......................................................................................................................3994.4 Roll screens........................................................................................................................401

4.4.1 Diamond pattern fines screen................................................................................4024.4.2 Pocket roll fines screen..........................................................................................404

4.5 Bar screens ........................................................................................................................4054.5.1 Optimize bar screens.............................................................................................406

4.6 Wave screens ....................................................................................................................4074.6.1 Flip flow screen......................................................................................................4074.6.2 Wave mat screen...................................................................................................408

4.7 Rechippers .........................................................................................................................4094.8 Slicers ...............................................................................................................................4104.9 Chip conditioners ...............................................................................................................411

4.9.1 Pyramid pattern chip conditioner ...........................................................................4134.9.2 Chip optimizer........................................................................................................414

5 Chip storage and transportation ....................................................................................4185.1 Chip piles............................................................................................................................4235.2 Automatic chip piles ...........................................................................................................4255.3 Chip silos............................................................................................................................4285.4 Aging chip silo ....................................................................................................................4295.5 Chip transport to storage....................................................................................................4325.6 Chip transport to digester...................................................................................................4455.7 Purchased chip handling....................................................................................................4526 Bark handling ...................................................................................................................4556.1 Bark dewatering .................................................................................................................4596.2 Bark screening ...................................................................................................................4606.3 Bark shredding ...................................................................................................................4616.4 Bark pressing .....................................................................................................................465

6.4.1 Cycle press ............................................................................................................4666.4.2 Multipress...............................................................................................................4676.4.3 Step press..............................................................................................................4686.4.4 Single-pass press ..................................................................................................468

6.5 Bark storage.......................................................................................................................4696.6 Bark transport.....................................................................................................................4707 Water handling .................................................................................................................4727.1 Circulation water system....................................................................................................4757.2 Thawing water system .......................................................................................................4758 Wood handling systems..................................................................................................4768.1 Wood handling plant layout................................................................................................4778.2 Woodroom layout ...............................................................................................................4798.3 Screening layout ................................................................................................................4798.4 Chip storage layout ............................................................................................................4818.5 Process control and personnel plan...................................................................................482

8.5.1 Process optimization..............................................................................................4838.5.2 Staffing plan...........................................................................................................485

8.6 Raw material ......................................................................................................................4868.6.1 Installation for cleaning and chipping of stumps....................................................4868.6.2 Whole tree chip cleaning process..........................................................................488



8.6.3 Pulp chip method ...................................................................................................489References.........................................................................................................................490

Chapter 5 - Batch cooking applications

1 Principles of displacement batch cooking....................................................................4942 Pulping performance of batch cooking .........................................................................4963 Description of displacement batch cooking operations..............................................5013.1 Displacement batch cooking plant .....................................................................................5013.2 Cooking cycle.....................................................................................................................5033.3 Heat recovery.....................................................................................................................5073.4 Soap separation .................................................................................................................5073.5 Malodorous gases..............................................................................................................5083.6 Control system ...................................................................................................................509

References.........................................................................................................................511

Chapter 6 - Continuous cooking applications

1 Introduction ......................................................................................................................5132 Industry standard for continuous pulping systems.....................................................5153 Overview description of process and equipment.........................................................5153.1 Pre-steaming......................................................................................................................5193.2 Chip metering and feeding process pressure ....................................................................5223.3 Top circulation lines and top separator ..............................................................................5283.4 Impregnation zone .............................................................................................................5303.5 Primary heating zone .........................................................................................................5323.6 Screen and screen header design .....................................................................................5363.7 Cooking and extraction zones............................................................................................5393.8 Countercurrent Hi-Heat washing........................................................................................5413.9 Blow dilution and cold blowing ...........................................................................................5443.10 Process gases....................................................................................................................5454 Modified cooking processes...........................................................................................5464.1 Isothermal cooking (ITC)....................................................................................................5494.2 Lo-Solids pulping................................................................................................................552

4.2.1 Process objectives.................................................................................................5524.2.2 Basic principles of Lo-Solids pulping .....................................................................5524.2.3 Configuration of process equipment......................................................................5534.2.4 Lo-Solids pulping in practice..................................................................................5534.2.5 Decreases in time and concentration profile of dissolved wood solids .................5534.2.6 Pulp strength, EA consumption, and bleachability ................................................5544.2.7 Digester extraction capacity and brownstock washing..........................................5554.2.8 Scaling and heat distribution..................................................................................555

5 Recent developments in the technology of continuous digesters.............................5565.1 Black liquor impregnation (BLI) ..........................................................................................5565.2 Diamondback chip bin........................................................................................................5595.3 Lo-Level feed system.........................................................................................................5636 Future developments in technology of continuous digesters ....................................566

References.........................................................................................................................569

Chapter 7 - Pulp washing applications

1 The atmospheric diffuser ................................................................................................573



1.1 Brownstock washing ..........................................................................................................5741.2 Post oxygen washing .........................................................................................................5741.3 Bleach plant washing .........................................................................................................5741.4 Design ...............................................................................................................................5751.5 Operation............................................................................................................................5761.6 Washing .............................................................................................................................5772 The pressure diffuser ......................................................................................................5772.1 Mechanical design and operating principle........................................................................578

2.1.1 The Ahlstrom design..............................................................................................5782.1.2 The Kvaerner design .............................................................................................579

2.2 Operating experiences .......................................................................................................5823 The Drum Displacer .........................................................................................................5823.1 Fractionated washing .........................................................................................................5823.2 Operating principle of DD washer ......................................................................................5843.3 Instrumentation ..................................................................................................................5853.4 Brownstock washing plant layout.......................................................................................5863.5 Brownstock washing experience........................................................................................5864 The GasFree filter.............................................................................................................5884.1 Special features of the GF washer.....................................................................................5884.2 Operating principle of the GF filter .....................................................................................5894.3 Instrumentation ..................................................................................................................5904.4 Layout ...............................................................................................................................5904.5 Applications........................................................................................................................5915 Press washing ..................................................................................................................5925.1 Wash press (Kvaerner) ......................................................................................................592

5.1.1 Design....................................................................................................................5925.1.2 Operation ...............................................................................................................5945.1.3 Washing .................................................................................................................594

5.2 Press washing (Sunds Defibrator) .....................................................................................5945.2.1 Displacement wash press......................................................................................5945.2.2 Wash systems .......................................................................................................596

5.3 The wash master wash press ............................................................................................5975.3.1 Basic mechanical design .......................................................................................5975.3.2 Operating principle.................................................................................................5985.3.3 Special features of the WM press..........................................................................5995.3.4 Layout ....................................................................................................................599

5.4 Instrumentation ..................................................................................................................600References.........................................................................................................................601

Chapter 8 - Pulp screening applications

1 Knot screening .................................................................................................................6192 Knot washing....................................................................................................................6213 Fine screening..................................................................................................................6223.1 Pressure screens ...............................................................................................................6224 Cleaners ............................................................................................................................6265 Screening system ............................................................................................................629

Chapter 9 - Bleaching applications

1 Equipment used in bleaching systems..........................................................................6171.1 Pumping and handling of medium-consistency fiber suspensions ....................................617



1.1.1 Fluidization.............................................................................................................6171.1.2 Air content..............................................................................................................6181.1.3 Medium consistency pumps ..................................................................................6181.1.4 Pumping applications.............................................................................................619

1.2 Mixing of chemicals and steam..........................................................................................6261.3 Reactors .............................................................................................................................6312 Post cooking delignification and bleaching stages .....................................................6342.1 Oxygen delignification ........................................................................................................635

2.1.1 Process parameters...............................................................................................6352.1.2 Oxygen stage systems ..........................................................................................6362.1.3 Post oxygen delignification washing......................................................................6372.1.4 Process optimization..............................................................................................640

2.2 Chlorine dioxide stages......................................................................................................6412.3 Alkaline extraction ..............................................................................................................6432.4 Hypochlorite bleaching stage.............................................................................................6452.5 Ozone stage.......................................................................................................................6452.6 Peroxide bleaching stage...................................................................................................6502.7 Chelation ............................................................................................................................6532.8 Acid hydrolysis ...................................................................................................................6542.9 Peracid stage .....................................................................................................................6552.10 Multi-chemical stages.........................................................................................................6553 Bleaching sequences ......................................................................................................6563.1 Chlorine chemical bleaching (CCB) ...................................................................................6563.2 Oxygen chemical bleaching (OCB)....................................................................................6624 Bleach plant liquid circulation closure ..........................................................................664

Chapter 10 - Pulp drying applications

1 Drying machine wet end..................................................................................................6671.1 Headbox.............................................................................................................................6701.2 Forming table .....................................................................................................................6711.3 Wire presses ......................................................................................................................6721.4 Press section......................................................................................................................6731.5 Drying machine accessories ..............................................................................................6732 Dryer section ....................................................................................................................6752.1 Pulp drying with airborne web............................................................................................675

2.1.1 Background............................................................................................................6752.1.2 Description.............................................................................................................6762.1.3 Drying of different pulp types.................................................................................6782.1.4 Cooling...................................................................................................................6792.1.5 Drying economy.....................................................................................................6792.1.6 Control ...................................................................................................................6812.1.7 Maintenance and service.......................................................................................681

2.2 Pulp flash drying.................................................................................................................6822.2.1 Background............................................................................................................6822.2.2 Description.............................................................................................................6822.2.3 Drying economy.....................................................................................................6842.2.4 Environmental aspects ..........................................................................................684

3 Pulp bale handling ...........................................................................................................684



Volume BChapter 11 - Chemical recovery

1 Overview of kraft recovery ..................................................................................................71.1 Kraft recovery unit operations ................................................................................................7

1.1.1 Evaporation................................................................................................................81.1.2 Recovery boiler ..........................................................................................................91.1.3 Lime kiln...................................................................................................................101.1.4 Causticizing..............................................................................................................10

1.2 Gasification...........................................................................................................................111.3 Direct alkali recovery............................................................................................................122 Properties of kraft recovery process streams ................................................................122.1 Black liquor properties..........................................................................................................12

2.1.1 Composition of black liquor......................................................................................132.1.2 Elementary analysis of black liquor dry solids .........................................................142.1.3 Heating value...........................................................................................................162.1.4 Density .....................................................................................................................182.1.5 Specific heat capacity ..............................................................................................192.1.6 Boiling point rise ......................................................................................................202.1.7 Thermal conductivity................................................................................................202.1.8 Viscosity...................................................................................................................212.1.9 Surface tension........................................................................................................24

2.2 Smelt properties ...................................................................................................................242.2.1 Enthalpy ...................................................................................................................242.2.2 Heat of formation .....................................................................................................252.2.3 Heat of reduction .....................................................................................................25

2.3 Flue gas and air properties ..................................................................................................262.3.1 Density .....................................................................................................................262.3.2 Enthalpy ...................................................................................................................282.3.3 Specific heat capacity ..............................................................................................282.3.4 Conductivity .............................................................................................................292.3.5 Viscosity...................................................................................................................30

2.4 Air .........................................................................................................................................312.5 Properties of green liquor.....................................................................................................322.6 Properties of miscellaneous chemical compounds..............................................................33

References...........................................................................................................................34

Chapter 12 - Evaporation of black liquor

1 General ................................................................................................................................372 Black liquor properties ......................................................................................................372.1 Composition of black liquor dry solids..................................................................................372.2 Physical properties of black liquors......................................................................................383 Principles of evaporation ..................................................................................................403.1 Multiple effect evaporation ...................................................................................................413.2 Vapor compression evaporation ..........................................................................................423.3 Flash steam evaporation......................................................................................................433.4 Evaporator plant coupling ....................................................................................................433.5 Concentrator coupling ..........................................................................................................453.6 Stripper column integration ..................................................................................................454 Evaporator design features...............................................................................................464.1 Rising film (RF) evaporator ..................................................................................................46



4.2 Falling film (FF) evaporators ................................................................................................47

4.3 Concentrators (first effect evaporators) ...............................................................................504.4 Evaporator plant auxiliary equipment...................................................................................514.5 Stripping column and menthol liquification...........................................................................534.6 Direct contact (DC) evaporator ............................................................................................555 Heat transfer .......................................................................................................................565.1 Heat transfer of evaporators ................................................................................................565.2 Heat transfer theory and calculation in multiple effect evaporation .....................................595.3 Heat balance ........................................................................................................................625.4 Evaporator calculation..........................................................................................................645.5 Multiple effect evaporation ...................................................................................................676 Evaporation systems and applications ...........................................................................726.1 Application of vapor compression evaporation (VCE) .........................................................726.2 Application of flash steam evaporation ................................................................................736.3 High solids concentrators.....................................................................................................756.4 Liquid heat treatment (LHT) method ....................................................................................766.5 Pressurized tank method .....................................................................................................786.6 Typical liquor specification for black liquor evaporation.......................................................797 Design .................................................................................................................................797.1 Evaporator plant design .......................................................................................................797.2 Storage tank design .............................................................................................................828 Soap skimming...................................................................................................................828.1 Soap separation theory ........................................................................................................838.2 Soap skimming procedures..................................................................................................859 Scaling of the heat transfer surfaces...............................................................................889.1 Scaling and heat transfer .....................................................................................................889.2 Reasons for scaling..............................................................................................................889.3 Types of scales ....................................................................................................................89

9.3.1 General ....................................................................................................................899.3.2 Calcium carbonate scaling.......................................................................................899.3.3 Calcium carbonate scale control..............................................................................899.3.4 Sodium carbonate and sulfate scaling.....................................................................909.3.5 Sodium carbonate and sulfate scale control............................................................919.3.6 Fouling by fiber and soap ........................................................................................919.3.7 Aluminum silicate scaling.........................................................................................919.3.8 Aluminum silicate scale control................................................................................92References...........................................................................................................................93

Chapter 13 - Recovery boiler

1 Evolution of recovery boiler design.................................................................................961.1 Two drum recovery boiler.....................................................................................................961.2 Modern recovery boiler ........................................................................................................971.3 Future recovery boilers ........................................................................................................992 Material and energy balance...........................................................................................1002.1 Material balance.................................................................................................................1002.2 Energy balances ................................................................................................................1042.3 High dry solids....................................................................................................................1053 Combustion of black liquor.............................................................................................1083.1 Drying ...............................................................................................................................1103.2 Devolitilization ....................................................................................................................1103.3 Char combustion ................................................................................................................111



3.4 Smelt reactions ..................................................................................................................112

3.5 Combustion of black liquor droplet in the furnace..............................................................1134 Dimensioning of boiler heat transfer surfaces .............................................................1144.1 Main design criteria ............................................................................................................1145 Boiler processes ..............................................................................................................1215.1 Air system...........................................................................................................................1215.2 Flue gas system .................................................................................................................1225.3 Water and steam................................................................................................................1226 Recovery boiler operation...............................................................................................1236.1 Soot blowing control...........................................................................................................1236.2 Enrichment of potassium and chlorides to dust .................................................................126

References.........................................................................................................................130

Chapter 14 - White liquor preparation

1 General ..............................................................................................................................1351.1 Characterization of the liquors ...........................................................................................1361.2 Recausticizing chemistry....................................................................................................1391.3 Chemical reactions in lime reburning.................................................................................1412 White liquor plant material balances .............................................................................1413 Sodium and sulfur balances ...........................................................................................1424 Environmental issues ......................................................................................................1445 Nonprocess elements in white liquor preparation .......................................................1455.1 Nonprocess elements in recausticizing..............................................................................1455.2 Nonprocess elements in lime reburning.............................................................................1475.3 Reducing NPE in the lime cycle.........................................................................................1496 Future challenges ............................................................................................................1507 Green liquor treatment ....................................................................................................1507.1 Separation of solid impurities .............................................................................................151

7.1.1 Clarification ............................................................................................................1527.1.2 Filtration .................................................................................................................154

7.2 Green liquor cooling ...........................................................................................................1577.3 Dregs handling ...................................................................................................................158

7.3.1 Dregs washer clarifier ............................................................................................1587.3.2 Vacuum precoat filtration .......................................................................................1587.3.3 Pressure disc precoat filtration ..............................................................................1597.3.4 Chamber filter press filtration.................................................................................159

8 Recausticizing ..................................................................................................................1618.1 General...............................................................................................................................1618.2 Process ..............................................................................................................................161

8.2.1 Slaking ...................................................................................................................1628.2.2 Causticizer train .....................................................................................................1648.2.3 White liquor separation ..........................................................................................1658.2.4 Storage tanks for white liquor and weak white liquor ............................................1708.2.5 Lime mud dewatering ............................................................................................1708.2.6 Modifications of white liquor...................................................................................172

8.3 Automation .........................................................................................................................1748.3.1 Process requirements............................................................................................174

8.4 Field instrumentation..........................................................................................................1748.5 Process controls.................................................................................................................175

8.5.1 Manual control .......................................................................................................1758.5.2 Conductivity measurement and control .................................................................175



8.5.3 Automatic process titrator and control ...................................................................176

8.5.4 Temperature difference control..............................................................................1788.5.5 Fuzzy control..........................................................................................................178

9 Lime reburning .................................................................................................................1789.1 Lime reburning process and equipment selection .............................................................179

9.1.1 Mechanical dewatering ..........................................................................................1809.1.2 Lime reburning process in the kiln.........................................................................1819.1.3 Brick lining..............................................................................................................1839.1.4 Firing equipment ....................................................................................................1849.1.5 Dust handling.........................................................................................................1859.1.6 Scrubber ................................................................................................................185

9.2 Limestone burning..............................................................................................................1869.2.1 Limestone quality...................................................................................................187

9.3 Material heat and balance..................................................................................................1879.3.1 Factors influencing heat balance...........................................................................188

9.4 Combustion ........................................................................................................................1909.4.1 Fuel oil and natural gas .........................................................................................1919.4.2 Noncondensible gases (NCG)...............................................................................1919.4.3 Tall oil and methanol..............................................................................................1929.4.4 Wood waste and other solid fuels..........................................................................193

9.5 Emissions ...........................................................................................................................1939.5.1 Formation of SO2, TRS, CO, particulate, and Nox................................................1949.5.2 Emission control ....................................................................................................195

9.6 Automation of rotating kiln..................................................................................................1969.6.1 Lime kiln field instrumentation ...............................................................................1969.6.2 Lime kiln control .....................................................................................................198

9.7 Maintenance.......................................................................................................................199References.........................................................................................................................201

Chapter 15 - Combustion of bark

1 Introduction ......................................................................................................................2051.1 Operating principle of steam boilers ..................................................................................2051.2 Cogeneration steam cycles................................................................................................2072 Physical and chemical properties of fuels ....................................................................2082.1 Fuels and their composition ...............................................................................................2082.2 General terminology and properties of fuels ......................................................................2082.3 Bark, wood, and hog fuel ...................................................................................................2123 Calculation of combustion..............................................................................................2143.1 Combustion reactions ........................................................................................................2143.2 Combustion air demand .....................................................................................................2153.3 Flue gas composition .........................................................................................................2173.4 Adiabatic temperature of combustion ................................................................................2193.5 Emissions from combustion ...............................................................................................2203.6 Heat transfer properties of flue gases................................................................................2234 Combustion technologies of bark..................................................................................2244.1 Grate firing..........................................................................................................................2244.2 Introduction to fluidized bed combustion............................................................................2274.3 Bubbling fluidized bed (BFB) combustion ..........................................................................2314.4 Circulating fluidized bed (CFB) combustion.......................................................................2334.5 Environmental aspects of fluidized bed combustion..........................................................2374.6 Gasification.........................................................................................................................239



5 Boiler processes ..............................................................................................................241

5.1 Handling of bark .................................................................................................................2415.2 Handling of auxiliary fuels ..................................................................................................2425.3 Air and flue gas circuit, fans ...............................................................................................2455.4 Dust separation methods for flue gas cleaning..................................................................2525.5 Feed water pumping ..........................................................................................................2555.6 Water-steam circuit ............................................................................................................2625.7 Main controls of boilers ......................................................................................................2666 Structure and design of boiler heat exchangers ..........................................................2686.1 Introduction.........................................................................................................................2686.2 Corrosion of heat delivery surfaces ...................................................................................2696.3 Furnace tubes ....................................................................................................................2716.4 Superheaters......................................................................................................................2726.5 Economizers (feed water preheaters)................................................................................2746.6 Air preheaters.....................................................................................................................2756.7 Cleaning of heat delivery surfaces.....................................................................................2776.8 Thermodynamic design of heat exchangers ......................................................................2817 Boiler efficiency and losses............................................................................................2897.1 Determining efficiency with the direct method ...................................................................2897.2 Determining efficiency with the indirect method.................................................................293

References.........................................................................................................................301

Chapter 16 - Heat and power co-generation

1 Introduction ......................................................................................................................3032 Heat and power demand in pulp and paper manufacturing ........................................3033 Heat and power demand of chemical pulp mills...........................................................3053.1 Wood yard..........................................................................................................................3063.2 Cooking ..............................................................................................................................3063.3 Washing and screening......................................................................................................3063.4 Bleaching............................................................................................................................3073.5 Bleach stock cleaning ........................................................................................................3073.6 Drying machine ..................................................................................................................3073.7 Evaporation ........................................................................................................................3083.8 Recovery boiler ..................................................................................................................3093.9 Causticizing and lime kiln...................................................................................................3113.10 Bleaching chemicals preparation .......................................................................................3113.11 Water and effluent..............................................................................................................3123.12 Power boiler .......................................................................................................................3123.13 Steam turbines and water cooling......................................................................................3123.14 Other ...............................................................................................................................3144 Heat and power balance of chemical pulp mill .............................................................3144.1 Installed power vs. demand ...............................................................................................3144.2 Heat generation..................................................................................................................3154.3 Heat and power balance ....................................................................................................3184.4 Steam turbines ...................................................................................................................3184.5 Back pressure power process............................................................................................3224.6 Co-generation alternatives .................................................................................................3265 Paper mills ........................................................................................................................3295.1 Heat and power balance of newsprint production..............................................................3305.2 Heat and power generation in SC and LWC production....................................................331



6 Time dependent variation in power demand.................................................................333

6.1 Variations in energy production .........................................................................................3346.1.1 Variations in power demand in industry.................................................................3356.1.2 Power balance drawings........................................................................................335

Chapter 17 - Secondary heat systems and pinch technology

1 Introduction ......................................................................................................................3372 Secondary heat ................................................................................................................3372.1 Definition of secondary heat...............................................................................................3372.2 Secondary heat production in the pulp mill ........................................................................338

2.2.1 Continuous cooking ...............................................................................................3382.2.2 Displacement batch cooking..................................................................................3402.2.3 Conventional batch cooking...................................................................................3412.2.4 Warm water production from surface condenser...................................................3432.2.5 Secondary condensates from evaporation ............................................................3442.2.6 Secondary heat production of hot water from drying machine ..............................3472.2.7 Lime kiln flue gas scrubber ....................................................................................3472.2.8 Production of hot water from drying machine ........................................................3472.2.9 Other secondary heat sources in pulp mill ............................................................349

2.3 Secondary heat consumption.............................................................................................3502.4 Optimizing of secondary heat system ................................................................................351

2.4.1 Optimizing of warm water production ....................................................................3512.4.2 Optimizing hot water production ............................................................................352

2.5 Mill wide secondary system ...............................................................................................3552.5.1 Design considerations ...........................................................................................3552.5.2 Water quality control ..............................................................................................3552.5.3 Secondary heat system applications .....................................................................356

3 Process integration techniques .....................................................................................3603.1 Basic principles of pinch technology ..................................................................................360

3.1.1 Composite curves ..................................................................................................3603.1.2 Grand composite curve..........................................................................................3643.1.3 Total site analysis ..................................................................................................3663.1.4 Advantages and limitations....................................................................................368

3.2 Process integration using mathematical programming techniques ...................................3683.2.1 Overview of techniques .........................................................................................3693.2.2 Advantages and limitations....................................................................................370

3.3 Exergy analysis ..................................................................................................................371References.........................................................................................................................373

Chapter 18 - Byproducts of chemical pulping

1 Turpentine.........................................................................................................................3752 Soap and tall oil................................................................................................................3782.1 Introduction.........................................................................................................................3782.2 Chemistry ...........................................................................................................................378

2.2.1 General ..................................................................................................................3782.2.2 Composition of tall oil.............................................................................................379

2.3 Soap recovery system design............................................................................................3792.3.1 Skimming and storage of soap ..............................................................................379



2.3.2 Soap handling ....................................................................................................................3812.4 Tall oil plant design ............................................................................................................382

2.4.1 Tall oil yield ............................................................................................................3822.4.2 Design parameters ................................................................................................3832.4.3 Selection of process ..............................................................................................3832.4.4 Selection of equipment ..........................................................................................3842.4.5 Tall oil handling and storage..................................................................................386

2.5 End use of tall oil products .................................................................................................3862.5.1 Typical tall oil products ..........................................................................................3862.5.2 Special tall oil products ..........................................................................................387

3 Other byproducts .............................................................................................................3873.1 Byproducts from acidic pulping ..........................................................................................387

References.........................................................................................................................389

Chapter 19 - Preparation and handling of bleaching chemicals

1 Manufacture and handling of chlorine...........................................................................3911.1 Preparation of chlorine caustic...........................................................................................3921.2 Chlorine gas handling ........................................................................................................3941.3 Handling of caustic soda ....................................................................................................3962 Manufacture of hypochlorite...........................................................................................3963 Generation and handling of chlorine dioxide................................................................3963.1 Short chemistry ..................................................................................................................3963.2 Generation systems ...........................................................................................................3973.3 Safe handling of chlorine dioxide .......................................................................................4024 Hydrogen peroxide ..........................................................................................................4024.1 Manufacture of hydrogen peroxide ....................................................................................4024.2 Peroxy acids.......................................................................................................................4035 Oxygen ..............................................................................................................................4045.1 Manufacture of oxygen.......................................................................................................4045.2 Transportation and handling of oxygen..............................................................................4056 Ozone ...............................................................................................................................4066.1 Ozone manufacture............................................................................................................406

References.........................................................................................................................409

Chapter 20 - Organosolv pulping

1 Introduction ......................................................................................................................4112 Organosolv pulping methods .........................................................................................4113 Delignification chemistry in organosolv processes.....................................................4124 Technical and economic demands on new processes ................................................4135 Alcell ...............................................................................................................................4146 Organocell.........................................................................................................................4167 IDE ...............................................................................................................................4188 ASAM ...............................................................................................................................4189 Methanol-reinforced kraft pulping..................................................................................42110 Acetosolv, Acetocell, and Formacell .............................................................................42111 Milox ...............................................................................................................................42312 Future of Organosolv processes....................................................................................425

References.........................................................................................................................427



Chapter 21 - Process calculations and simulation

1 Simulation principles.......................................................................................................4292 General structure of a simulator ....................................................................................4303 Applications......................................................................................................................434

Chapter 22 - Closed cycle systems for manufacture of bleached chemical wood pulp

1 Introduction ......................................................................................................................4412 The effluent-free mill........................................................................................................4422.1 Concept ..............................................................................................................................4422.2 The first commercial application.........................................................................................4432.3 Lessons and projected requirements.................................................................................4463 System aspects ................................................................................................................4473.1 Basic technologies .............................................................................................................4473.2 Water, chemical, and energy balances..............................................................................4493.3 Nonprocess elements ........................................................................................................4553.4 Economics..........................................................................................................................4564 Mill-scale developments..................................................................................................4574.1 Champion International Corporation, Canton Mill ..............................................................4574.2 Louisiana-Pacific Corporation, Samoa Mill ........................................................................4594.3 Union Camp Corporation, Franklin Mill ..............................................................................4604.4 Modo, Husum Mill ..............................................................................................................4614.5 Munksjö Ab, Aspa Bruk Mill ...............................................................................................4624.6 Södra Cell, Värö Mill ..........................................................................................................4634.7 SCA, Östrand Mill...............................................................................................................4634.8 Metsä-Rauma, Rauma Mill.................................................................................................4635 Relevant technologies under development...................................................................4646 Minimum impact mill concepts.......................................................................................465

References.........................................................................................................................469

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Chemical Pulping