PSE 476: Lecture #11 Pulping and Bleaching PSE 476 Lecture #1 Introduction Lecture #1 Introduction.

PSE 476: Lecture #1 1

Pulping and BleachingPSE 476

Lecture #1Introduction

Lecture #1Introduction


Introduction to Pulping:History of Papermaking

• 3000 BC: Papyrus» Exterior of reed is laminated and pressed to

form sheet» Developed by Egyptians» Word paper derived from papyrus

• Making of papyrus

• 3000 BC: Papyrus» Exterior of reed is laminated and pressed to

form sheet» Developed by Egyptians» Word paper derived from papyrus

• Making of papyrus http://www.lib.umich.edu/pap/exhibits/papyrus_making/slides.html


Papyrus Making-Harvesting


Papyrus Making-Peeling


Papyrus Making-Cutting


Papyrus Making-Soaking


Papyrus Making-Rolling


Papyrus Making-Pressing, Drying


Papyrus Making-Final Product



• 200 BC: Parchment» Tanned skin of animals» Today parchment refers to high quality paper from

vegetable fibers

• 105 AD: Paper from plant (mulberry) fibers» Developed by Chinese Emperor by Ts'ai Lun» National secret stolen by Arabs in ~700 AD

• 1796: First continuous paper machine developed near Paris. Fiber source - rags (cotton)

• 200 BC: Parchment» Tanned skin of animals» Today parchment refers to high quality paper from

vegetable fibers

• 105 AD: Paper from plant (mulberry) fibers» Developed by Chinese Emperor by Ts'ai Lun» National secret stolen by Arabs in ~700 AD

• 1796: First continuous paper machine developed near Paris. Fiber source - rags (cotton)



• 1854: Soda pulping process developed in England

• 1840: Groundwood pulping developed in Germany

• 1867: Sulfite (acid) pulping process developed in US

• 1884: Kraft pulping process developed in Germany

• 1854: Soda pulping process developed in England

• 1840: Groundwood pulping developed in Germany

• 1867: Sulfite (acid) pulping process developed in US

• 1884: Kraft pulping process developed in Germany


Introduction to Pulping:Two Ways to Generate Fibers

• Mechanically: “Grind up” raw material (most of the lignin retained).» Newsprint

• Chemically: Dissolve away the lignin» Kraft pulping: NaOH/NaSH (dominant process)» Sulfite: (Sulfur Dioxide/bisulfite/sulfite) (limited number of

mills)» Other: Organosolv, steam explosion, etc (very minor)

• In this class, we are going to discuss the methods and chemistry used in the processes which convert fibrous materials to bleached fibers.

• Mechanically: “Grind up” raw material (most of the lignin retained).» Newsprint

• Chemically: Dissolve away the lignin» Kraft pulping: NaOH/NaSH (dominant process)» Sulfite: (Sulfur Dioxide/bisulfite/sulfite) (limited number of

mills)» Other: Organosolv, steam explosion, etc (very minor)

• In this class, we are going to discuss the methods and chemistry used in the processes which convert fibrous materials to bleached fibers.


Raw Material

• Fibrous material can come in the form of:» Wood (main form in the United States)» Other plant material (straw, reeds, etc)

• Wood» Softwoods & hardwoods» Logs (chipped directly from logs for pulp

production)» Chips (residuals from saw mill operations)

• Fibrous material can come in the form of:» Wood (main form in the United States)» Other plant material (straw, reeds, etc)

• Wood» Softwoods & hardwoods» Logs (chipped directly from logs for pulp

production)» Chips (residuals from saw mill operations)


Regional Affects on Raw Material

For this lecture,we will be lookingat raw material useby these regions.


Raw Material Log/Chip Makeup

Region Roundwood(%)

Residual(%)

Softwood(%)

Hardwood(%)

Totalcords*103

W. 38 62 92.5 7.5 10,420

N.C. 86.5 13.5 28 72 6,715

S. C. 71 29 63 37 39,137

N. E. 78 22 40 60 6,902

S. E. 74 26 73 27 29,387

Region Roundwood(%)

Residual(%)

Softwood(%)

Hardwood(%)

Totalcords*103

W. 38 62 92.5 7.5 10,420

N.C. 86.5 13.5 28 72 6,715

S. C. 71 29 63 37 39,137

N. E. 78 22 40 60 6,902

S. E. 74 26 73 27 29,387


Raw Material Log/Chip Makeup

Roundwoodmaterials * 103M3

(%) Residualmaterials * 103M3

(%)

1953 60,661 92 4,937 8

1996 145,170 71 60,341 29

Softwoodmaterials * 103M3

(%) Hardwoodmaterials * 103M3

(%)

1953 54,006 82 11,592 18

1996 136,072 65 72,439 35

Roundwoodmaterials * 103M3

(%) Residualmaterials * 103M3

(%)

1953 60,661 92 4,937 8

1996 145,170 71 60,341 29

Softwoodmaterials * 103M3

(%) Hardwoodmaterials * 103M3

(%)

1953 54,006 82 11,592 18

1996 136,072 65 72,439 35


Raw Material HandlingPhysical Measurements

• Physical measurements important for:» Determining how much wood is coming into the

mill.» How much wood is being charged into the

digesters.» How much actual wood mass (dry) is being

charged so to get the correct liquor to wood ratio.

• Mills use scales and other devices » Moisture content meters» Laboratory chip screening» Wood species determination

• Physical measurements important for:» Determining how much wood is coming into the

mill.» How much wood is being charged into the

digesters.» How much actual wood mass (dry) is being

charged so to get the correct liquor to wood ratio.

• Mills use scales and other devices » Moisture content meters» Laboratory chip screening» Wood species determination



• Moisture Content - Green (paper industry)» Wet basis, amount of water in wood as a fraction of

wet weight of wood

» Typical MCgr of freshly cut wood = 50% (30-60%)

• Moisture Content - Green (paper industry)» Wet basis, amount of water in wood as a fraction of

wet weight of wood

» Typical MCgr of freshly cut wood = 50% (30-60%)

MC gr =Mass of water in wood

Wet wood mass

• Moisture Content - Oven Dry (wood scientists/foresters)» Oven dry basis

» Typical MCOD of freshly cut wood = 100% (45-150%)

• Moisture Content - Oven Dry (wood scientists/foresters)» Oven dry basis

» Typical MCOD of freshly cut wood = 100% (45-150%)

Mass of water in woodOven dry wood mass

MC OD =

x 100%

x 100%



• Solid Wood Density• Solid Wood Density

» Wood contracts 8-15% on volume basis when it dries below 30% moisture. This needs to be taken into account when determining density.

» Typical units lb/ft3 or kg/m3

» Wood contracts 8-15% on volume basis when it dries below 30% moisture. This needs to be taken into account when determining density.

» Typical units lb/ft3 or kg/m3

Dry weight of woodDensity =

Unit volume of green wood


Raw Material HandlingDebarking and Chipping

• There are many different mechanical systems used to debark and chip wood. We will not cover these in this class. There are plenty of references available for you to read. Important points:» Get all of the bark of the log.» Bark typically used as fuel source.» Chip to a very consistent size.

• There are many different mechanical systems used to debark and chip wood. We will not cover these in this class. There are plenty of references available for you to read. Important points:» Get all of the bark of the log.» Bark typically used as fuel source.» Chip to a very consistent size.


Raw Material HandlingChip Dimensions

• Uniform Chip Size is very important!» Large chips undercook

leaving shives (rejects).» Small chips clog liquor

circulation, use large amount of chemicals, and give a low yield of weak pulp.

» Chip thickness the primary concern.

• Uniform Chip Size is very important!» Large chips undercook

leaving shives (rejects).» Small chips clog liquor

circulation, use large amount of chemicals, and give a low yield of weak pulp.

» Chip thickness the primary concern.

TOP

1/2 to 1” long

Var

iabl

e W

idth

Side

1/8 to 1/4” thick


Raw Material HandlingWood Deterioration

• Wood decay requires moisture and oxygen.» Moisture content > 20% MCOD.

» Remove either and slow/stop degradation.» Sprinkle solid wood (logs) with water to keep

the wood saturated and therefore limit oxygen content.

» Drying wood to <20% MCOD would slow degradation.

- Economically unsound.- Would slow liquor penetration and therefore

pulping.

• Wood decay requires moisture and oxygen.» Moisture content > 20% MCOD.

» Remove either and slow/stop degradation.» Sprinkle solid wood (logs) with water to keep

the wood saturated and therefore limit oxygen content.

» Drying wood to <20% MCOD would slow degradation.

- Economically unsound.- Would slow liquor penetration and therefore

pulping.


Raw Material HandlingChip Pile Degradation

• Conditions that accelerate degradation.

» Tall chip piles » Chip pile compaction» Whole tree chips» Storage of hardwoods (high starch

contents).

• Method to reduce degradation.» FIFO (first in first out)

• Conditions that accelerate degradation.

» Tall chip piles » Chip pile compaction» Whole tree chips» Storage of hardwoods (high starch

contents).

• Method to reduce degradation.» FIFO (first in first out)


Raw Material HandlingDeterioration in Wood Chip Piles

• General rule of thumb:» 1% loss to decay/month.

• Respiration of parechyma cells responsible for heat generation.

• Above 45-55°C, fungal and bacterial degradation stop.

• Chemical autoxidation takes over above 55°C. This results in severe losses during pulping.

• Loss of extractives high during storage.

• General rule of thumb:» 1% loss to decay/month.

• Respiration of parechyma cells responsible for heat generation.

• Above 45-55°C, fungal and bacterial degradation stop.

• Chemical autoxidation takes over above 55°C. This results in severe losses during pulping.

• Loss of extractives high during storage.


Raw Material HandlingDebris

• Debris is not a good thing!• Sources

» Bark, foliage, plastic, metals, dirt, decayed wood

• Problems» Dirt specks, loss of strength, structural

imperfections, wear on equipment.

• Debris is not a good thing!• Sources

» Bark, foliage, plastic, metals, dirt, decayed wood

• Problems» Dirt specks, loss of strength, structural

imperfections, wear on equipment.


Raw Material HandlingScreening

• Most mills use a screening system to achieve relative consistency in chip size.» Overs: Chips which are oversized

or over thick.» Accepts: Chips that are in the

correct size distribution.» Fines: Chips that are too small

(includes sawdust).

• Most mills use a screening system to achieve relative consistency in chip size.» Overs: Chips which are oversized

or over thick.» Accepts: Chips that are in the

correct size distribution.» Fines: Chips that are too small

(includes sawdust).

PSE 476: Lecture #11 Pulping and Bleaching PSE 476 Lecture #1 Introduction Lecture #1 Introduction.

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