- •Recovered Paper and Recycled Fibers
- •Isbn: 3-527-30999-3
- •Introduction
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •2006, Isbn 3-527-30997-7
- •Volume 1
- •Isbn: 3-527-30999-3
- •4.1 Introduction 109
- •4.2.5.1 Introduction 185
- •4.3.1 Introduction 392
- •5.1 Introduction 511
- •6.1 Introduction 561
- •6.2.1 Introduction 563
- •6.4.1 Introduction 579
- •Volume 2
- •7.3.1 Introduction 628
- •7.4.1 Introduction 734
- •7.5.1 Introduction 777
- •7.6.1 Introduction 849
- •7.10.1 Introduction 887
- •8.1 Introduction 933
- •1 Introduction 1071
- •5 Processing of Mechanical Pulp and Reject Handling: Screening and
- •1 Introduction 1149
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •Introduction
- •Introduction
- •Isbn: 3-527-30999-3
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •150.000 Annual Fiber Flow[kt]
- •1 Introduction
- •1 Introduction
- •Introduction
- •Isbn: 3-527-30999-3
- •Void volume
- •Void volume fraction
- •Xylan and Fiber Morphology
- •Initial bulk residual
- •4.2.5.1 Introduction
- •In (Ai) Model concept Reference
- •Initial value
- •Validation and Application of the Kinetic Model
- •Inititial
- •Viscosity
- •Influence on Bleachability
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Introduction
- •International
- •Impregnation
- •Influence of Substituents on the Rate of Hydrolysis
- •140 116 Total so2
- •Xylonic
- •Viscosity Brightness
- •Xyl Man Glu Ara Furf hoAc XyLa
- •Initial NaOh charge [% of total charge]:
- •Introduction
- •Isbn: 3-527-30999-3
- •Introduction
- •Isbn: 3-527-30999-3
- •Introduction
- •Introduction
- •Isbn: 3-527-30999-3
- •In 1950, about 50% of the global paper production was produced. This proportion
- •4.0% Worldwide; 4.2% for the cepi countries; and 4.8% for Germany.
- •1150 1 Introduction
- •1 Introduction
- •1 Introduction
- •Virgin fibers
- •74.4 % Mixed grades
- •Indonesia
- •Virgin fibers
- •Inhomogeneous sample Homogeneous sample
- •Variance of sampling Variance of measurement
- •1.Quartile
- •3.Quartile
- •Insoluble
- •Insoluble
- •Insoluble
- •Integral
- •In Newtonion liquid
- •Velocity
- •Increasing dp
- •2Α filter
- •0 Reaction time
- •Increasing interaction of probe and cellulose
- •Increasing hydrodynamic size
- •Vessel cell of beech
- •Initial elastic range
- •Internal flow
- •Intact structure
- •Viscosity 457
- •Isbn: 3-527-30999-3
- •1292 Index
- •Visbatch® pulp 354
- •Index 1293
- •1294 Index
- •Impregnation 153
- •Viscosity–extinction 433
- •Index 1295
- •1296 Index
- •Index 1297
- •Inhibitor 789
- •1298 Index
- •Index 1299
- •Impregnation liquor 290–293
- •1300 Index
- •Industries
- •Index 1301
- •1302 Index
- •Index 1303
- •Xylose 463
- •1304 Index
- •Index 1305
- •1306 Index
- •Index 1307
- •1308 Index
- •In conventional kraft cooking 232
- •Visbatch® pulp 358
- •Index 1309
- •In prehydrolysis-kraft process 351
- •Visbatch® cook 349–350
- •1310 Index
- •Index 1311
- •1312 Index
- •Viscosity 456
- •Index 1313
- •Viscosity 459
- •Interactions 327
- •1314 Index
- •Index 1315
- •Viscosity 459
- •1316 Index
- •Index 1317
- •Xylose 461
- •Index 1319
- •Visbatch® pulp 355
- •Impregnation 151–158
- •1320 Index
- •Index 1321
- •1322 Index
- •Xylan water prehydrolysis 333
- •Index 1323
- •1324 Index
- •Viscosity 459
- •Index 1325
- •Xylose 940
- •1326 Index
- •Index 1327
- •In selected kinetics model 228–229
- •4OMeGlcA 940
- •1328 Index
- •Index 1329
- •Intermediate molecule 164–165
- •1330 Index
- •Viscosity 456
- •Index 1331
- •1332 Index
- •Impregnation liquor 290–293
- •Index 1333
- •1334 Index
- •Index 1335
- •1336 Index
- •Impregnation 153
- •Index 1337
- •1338 Index
- •Viscose process 7
- •Index 1339
- •Volumetric reject ratio 590
- •1340 Index
- •Index 1341
- •1342 Index
- •Index 1343
- •1344 Index
- •Index 1345
- •Initiator 788
- •Xylose 463
- •1346 Index
- •Index 1347
- •Vessel 385
- •Index 1349
- •1350 Index
- •Xylan 834
- •1352 Index
Impregnation
COUNTERCURRENT
COOKING
CONCURRENT
COOKING
EXTENDED / ITC
COOKING
Extraction
liquor
White liquor
DILUTION /
DISCHARGE
STEAMING
Energy,
white liquor
Energy,
white liquor,
wash filtrate
CHIPS
LIQUOR LIQUOR
Energy,
white liquor
Fig. 4.145 Typical EMCC/ITC process steps and flow regime.
4.2 Kraft Pulping Processes 387
ITC systems have been expanded with black liquor impregnation, where a part
of the extraction liquor from the cooking zone supports impregnation before
being drawn from a separate extraction screen within the impregnation zone [12].
4.2.8.3.6 Lo-Solids Cooking
As indicated by the name, the Lo-Solids concept [14,15]adds the feature of
reduced dry solids concentration to continuous cooking. The main reduction of
solids is achieved by the extraction of dissolved organic substances after impregnation
and by addition of wash filtrate to the cooking zones. Compared to EMCC,
Lo-Solids pulping further improves the uniform distribution of alkali and temperature
over the cook.
A typical configuration of a Lo-Solids retrofit to a single-vessel hydraulic digester
is shown in Fig. 4.146. The first screen section, often the former upper cooking
circulation (UCC) section, is used for extraction of spent cooking chemicals and
of wood material dissolved during the impregnation step. It must be remembered
that 20–30% of the total wood substance is dissolved, and a considerable amount
of alkali is consumed during impregnation. Below the first extraction at the UCC
Steam
Pulp
Extraction
liquor
Wash filtrate
Circulation transfer
White liquor
Extraction
liquor
Extraction
liquor
Fig. 4.146 Typical Lo-Solids single-vessel hydraulic digester [14,15].
388 4 Chemical Pulping Processes
screens follows a short countercurrent impregnation and heating zone down to
the second screen section, often the former lower cooking circulation screens.
White liquor and wash filtrate are added to the circulation liquor and heated to
full cooking temperature.
Subsequently, the chips move into a concurrent and a countercurrent cooking
zone separated by the second extraction, before proceeding into the extended
cooking zone (Fig. 4.147). The third extraction occurs at the fourth set of screens.
Only a part of the liquor taken from the screen is extracted, while the remainder
is made up with alkali and wash filtrate and returned to the central pipe discharge.
The pulp continues to travel down through the countercurrent extended
cooking zone and is finally diluted and discharged. Compared to the retrofit
arrangement described above, a new Lo-Solids installation would omit the fourth
set of screens and respective liquor circulation.
COUNTERCURRENT
COOKING
CONCURRENT
Impregnation
CONCURRENT
COOKING
COUNTERCURRENT
Impregnation
AND HEATING
EXTENDED
COOKING
Extraction
liquor
White liquor
DILUTION /
DISCHARGE
STEAMING
Energy,
white liquor,
wash filtrate
CHIPS
LIQUOR LIQUOR LIQUOR
Extraction
liquor
LIQUOR
Energy,
white liquor,
wash filtrate
Energy,
white liquor,
wash filtrate
Extraction
liquor
LIQU.
Fig. 4.147 Typical Lo-Solids process steps and flow regime [14].
4.2 Kraft Pulping Processes 389
390 4 Chemical Pulping Processes
The application of Lo-Solids pulping has led to reduced white liquor consumption
and improved washing efficiency in the digester. The latter can be attributed
mostly to higher extraction liquor flow rates. When running on a single extraction,
overloaded systems often experience screen limitations and countercurrent
flow restrictions. In such cases, when the digester cannot deal with the full quantity
of wash filtrate, the excess filtrate must by-pass the digester to the evaporation
plant. Such filtrate is lost for washing. Multiple extractions allow a larger total
flow of extracted liquor without excessive load on screens, and multiple wash filtrate
addition reduces the relative velocity of liquor and chip column in countercurrent
zones. It has been found that the improved chip movement, when
coupled with the increased extraction capacity, has boosted not only the washing
efficiency but also the digester capacity.
Further information regarding the general technological aspects of continuous
cooking is provided in Sections 4.2.8.3.4 and 4.2.8.3.5.
The Lo-Solids concept is undergoing continuing refinement in terms of accommodation
to cooking chemistry and reduced installation efforts. Someof the related technologies
are specifically addressing the requirements of a particular cooking application.
EnhancedAlkali Profile Cooking (EAPC) uses black liquor fromthe lower extraction,
together with white liquor, for impregnation [16,17]. The widely simplified process
configuration of the Downflow Lo-Solids concept is shown in Fig. 4.148.
Steam
Wash filtrate
Circulation transfer
White liquor
FILTRATE
PREHEATER
COOKING
HEATER
Pulp
Extraction liquor
Steam
Extraction liquor
Fig. 4.148 Typical Downflow Lo-Solids single-vessel hydraulic digester [8].
4.2.8.3.7 Heat Recovery Systems
Usually, heat is recovered from the extraction liquor for the generation of vapor to
be used in chip steaming. The conventional heat recovery system consisting of
two flash tanks installed in series is shown schematically in Fig. 4.149. Flash tank
1 is operated at a pressure of about 1.5 bar(g), and delivers flash steam to the pressurized
steaming vessel. Flash tank 2 feeds the atmospheric chip bin, and is pressure-
controlled at a small overpressure. The flash tanks are equipped with internals
which reduce foaming by providing a special flow pattern and generous
liquor surface. Any flash steam not needed for steaming is condensed, with the noncondensable
gases transferred to the mill’s gas collection and treatment system.
Extraction liquor
Weak liquor
Flash steam to
steaming vessel
Flash steam
to chip bin
FLASH
TANK 2
FLASH
TANK 1
Fig. 4.149 Conventional heat recovery system.
The Lo-Level heat recovery system by Andritz (Fig. 4.150) generates clean steam
from feed water by indirect heat exchange in a reboiler. The clean steam eliminates
emissions of reduced sulfur compounds (TRS) from chip steaming operations.
On the other hand, the water evaporation requirements and the TRS load
increase in the evaporation plant.
Weak liquor
Clean steam
to chip bin
Feed water
Extraction liquor
REBOILER
Fig. 4.150 The Andritz Lo-Level heat recovery system [8].
Modern heat recovery systems may also include indirect heat exchange between
extraction liquor and cool process liquors, with the goal of improving the steam
economy. Examples are the heating of white liquor before injection into a cooking
circulation, or the heating of wash filtrate in a Lo-Solids cooking system.
4.2 Kraft Pulping Processes 391
4.3
Sulfite Chemical Pulping
Herbert Sixta
4.3.1