Pulping and Bleaching PSE 476

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Pulping and BleachingPSE 476

• Lecture 1
• Introduction

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Introduction to PulpingHistory 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

http//www.lib.umich.edu/pap/exhibits/papyrus_maki
ng/slides.html
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Papyrus Making-Harvesting
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Papyrus Making-Peeling
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Papyrus Making-Cutting
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Papyrus Making-Soaking
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Papyrus Making-Rolling
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Papyrus Making-Pressing, Drying
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Papyrus Making-Final Product
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Introduction to PulpingHistory of Papermaking

• 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)

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Introduction to PulpingHistory of Papermaking

• 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

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Introduction to PulpingTwo 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.

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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)

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Regional Affects on Raw Material
For this lecture, we will be looking at raw
material use by these regions.
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Raw Material Log/Chip Makeup
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Raw Material Log/Chip Makeup
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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

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Raw Material HandlingPhysical Measurements

• 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)

Mass of water in wood
MC gr
x 100
Wet wood mass

• Moisture Content - Oven Dry (wood
  scientists/foresters)
• Oven dry basis
• Typical MCOD of freshly cut wood 100 (45-150)

Mass of water in wood
MC OD
x 100
Oven dry wood mass
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Raw Material HandlingPhysical Measurements

• Solid Wood Density

Dry weight of wood

• 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

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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.

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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.

1/8 to 1/4 thick
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Raw Material HandlingWood Deterioration

• Wood decay requires moisture and oxygen.
• Moisture content gt 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 lt20 MCOD would slow degradation.
• Economically unsound.
• Would slow liquor penetration and therefore
  pulping.

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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)

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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 45-55C, fungal and bacterial degradation
  stop.
• Chemical autoxidation takes over above 55C.
  This results in severe losses during pulping.
• Loss of extractives high during storage.

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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.

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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).