wood and pulp

| Wood and Pulp | Sappi Fine Paper Europe1

Wood and pulp


Contents

1. Wood types 31.1. Wood structure 61.2. Wood growth 71.3. Cellulose formation 81.4. Chemical composition 9

2. Pulp production 102.1. Woodyard 112.2. Debarking 122.3. Chipping 132.4. Defibring 14

2.4.1. Mechanical vs. chemical pulp 152.4.2. Mechanical pulp 162.4.3. Chemical pulp 19

2.5. Measurement data 242.6. Bleaching 25

2.6.1. Bleaching methods 27

3. Overview pulp mill Sappi Gratkorn 28


1. Wood types

Woodtypes

Deciduous(Hardwood)

Beech

Birch

Poplar

Coniferous(Softwood)

Spruce

Pine

Fir

Typed


1. Wood types

HardwoodShort fibres

SoftwoodLong fibres

• Structure


1. Wood types

Deciduous woordShort fibre

Nconiferous woodzLong fibre

Firmness Medium High

Flexibility Medium High

Bulk/Volume High Medium

Opacity High Medium

Suited for High g/m² Low g/m²

Fibre length 1 mm 2-3 mm

Fibre width 15-25 µm 35-45 µm

Characteristics for paper mixture (pulp)

Basics: The magic is in the mixture


1.1. Wood structure• Bark:

– Outer layer consisting of dead cork cells– Protection against damage, loss of water, weather, bacteria– Bark cells do not grow, they burst

• Cork cambium:– Builds cork cells and thus, the bark– Closes tears in the bark coat

• Phloem (Inner bark)– Storage and transport of substances for the process of assimilation

Assimilation = Conversion of substance and energy• Cambium:

– The living, growing part of the tree• Sapwood:

– Transport of water and nutrients, strengthening and assimilation substance storage– One new ring is formed every year (in seasonally affected phases)– Storage of lignin (gum)

• Heartwood:– Supporting column, which usually starts to grow at a tree age of 20-40 years

• Pith:– Dead fibre tissue, the core of the tree trunk


1.2. Wood growth

SpringCambium splitsoff thin-walledcells: spring

wood

Broad growthrings

SummerCambium splitsoff thick-walledcells: summer

wood

Narrow growthrings

Winter No growth No ringformation

• Growth periods depending on climate and location


1.3. Cellulose formation

– Grape sugar (glucose) is converted to starch by shedding water– As it multiplies, cellulose is formed


1.4. Chemical composition

• Cellulose:– Primary cell wall substance– Long, fibrous polysaccharide chain of glucose molecules– Hydrogen bonding builds a crystalline structure

• Hemicellulose:– Sealants and flexibilisators– Short polysaccharide chain consisting of various sugars

• Lignin:– Wood glue– Filling substance in the cellulose frame– Wood formation initiator– Absorbs pressure, protects agains attacks


2. Pulp productionProcess


2.1. Wood yardStep 1


2.2. DebarkingStep 2: Debarking drum


2.3. ChippingStep 3


2.4. DefibringStep 4


2.4.1. Mechanical vs. chemical pulp

Mechanical pulp Chemical pulp

Cost Low High

Yield High: approx. 90% Low: approx. 50%

Chemicals Few Many (re-usable >99%)

Energy Intensive Energy generation

Brightness Low High

Yellowing High Low

Opacity High Low

Stiffness Low High


2.4.2. Mechanical pulp

• Stone groundwood (SGW)– Developed1843 by F. G. Keller– No pre-processing– Processing under atmospheric pressure and temperature– Yield: 90-95% All wood components are fully maintained

• Brown groundwood– Vaporization before grinding– Fibres have brownish colour– Yield: <90% But better stiffness

• Pressurized groundwood (PGW)– Processing under pressure (2 to 4.5 bar) and high temperature (110-135°C)

• Chemical groundwood (CGW)– Chemical pre-processing– Lignin is partially removed Low yield

Wood containing


2.4.2. Mechanical pulp

• TMP– Wood chips are vaporized– Chips are ground down to single fibres in refiners, under vapour pressure

• CTMP– Wood chips are impregnated (mixed with a chemical substance)– Cooked– Ground– Bleached

(Chemi) Thermo Mechanical Pulp


2.4.2. Mechanical pulp(Chemi) Thermo Mechanical Pulp

C: chemicalimpregnationof woodchips

T: light cooking ofwoodchips

M: mechanical refining

P: pulpready forbleaching


2.4.3. Chemical pulp

• Purpose:– Stripping and dissolving lignin Lignin is what holds the individual fibres together

– Maintaining the cellulose fibre structure

• In practice:– Only residual lignin remains– Hemicelullose and cellulose are also partially removed– Yield is approx. 50% (mechanical pulp approx. 90%)

• Main types:– Sulphate pulp– Sulphite pulp



Sulphate pulp(kraft pulp) Sulphite pulp

Cooking time 1-2 hours 3-8 hours

Temperature 170-180°C 130-140°C

pH-value 13+ (alkaline) 1-2 (acidic)

Yield 45-50% 50-55%

Stiffness HighFibres assailed from outside

LowFibres assailed from within

Raw materials Flexible Limited

Cost High Low

Odour Heavy Neutral



• Developed 1879– 80 – 85 % of all pulp production worldwide

• Basic materials:– Roundwood and wood chips

• Alkaline cooking process: pH value 11

• Special features:– Suitable for all wood types, including annuals– Obligatory recycling of used chemicals– Energy generation from burnt waste

Sulphate pulp



• Developed 1876 - 1878– 15 – 20 % of all pulp production worldwide

• Basic materials:– Roundwood and wood chips

• Acidic cooking process: pH value 4– Cooking time 3-8 hours in sulphurous acids (magnesium bisulphite)– Lignin is washed out in acidic environment– Defibring under pressure at 130-145°C– Requires high quality wood– Yield approx. 55%

• Special features:– Not suitable for resinous wood types (pine)– Recent regulations make recycling of used chemicals obligatory

Sulphite pulp



Advantages Disadvantages

Cost-effective use of small units from Sulphite: 100,000 tons per year Sulphate: 500,000 tons per year

Limited raw material base

Good yield Bark sensitive

Good bleaching characteristics Low stiffness

High basic whiteness Sulphite: greyish white / Sulphate: brown

High burden on waste water

Sulphite pulp


2.5. Measurement data

Pulp hardness Kappa Residual ligninVery soft 0.5 – 1 1.5%Soft 11 – 15 1.5 – 2.5%Normal 23 – 31 3.0 – 4.0%Hard 46 – 54 6.0 – 7.0%Very hard 54 – 69 7.0 – 9.0%


2.6. Bleaching

• Modification of coloured substances in the pulp– Coloured substances lose the ability to fully absorb light– Residual lignin and other undesired substances are removed

Cooking O₂ Bleaching


2.6. Bleaching

• Intermediate washing phases during chemical treatment

First washing phase Last washing phase


2.6.1. Bleaching methods

• Pulp can be bleached with:– Elemental chlorine and chlorine dioxide In the past Highly negative effects on the environment Modern ECF/TCF pulp Elemental Chlorine Free/Totally Chlorine Free

– Ozone (O3) and oxygen (O₂) in various forms Resulting paper is virtually odour free Sappi was the first paper producer to use the „Sapoxal oxygen bleach process“

– Hydrogen peroxide (H₂O₂) Components: caustic soda, water glass, sulphuric acid Oxidative process: metal + oxygen is converted to metal oxide

– Natriumdithionit (NaS₂O4) Reductive process: metal oxide is dissolved into metal + oxygen


3. Overview pulp factory Sappi Gratkorn


Thank youfor your attention

Jörg Abelmann