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

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Pulping and BleachingPSE 476

Lecture #1

Introduction

PSE 476: Lecture #1


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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

http://www.lib.umich.edu/pap/exhibits/papyrus_making/slides.html

PSE 476: Lecture #1


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Papyrus Making-Harvesting

PSE 476: Lecture #1


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Papyrus Making-Peeling

PSE 476: Lecture #1


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Papyrus Making-Cutting

PSE 476: Lecture #1


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Papyrus Making-Soaking

PSE 476: Lecture #1


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Papyrus Making-Rolling

PSE 476: Lecture #1


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Papyrus Making-Pressing, Drying

PSE 476: Lecture #1


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Papyrus Making-Final Product

PSE 476: Lecture #1


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Introduction to Pulping:History 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)

PSE 476: Lecture #1


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Introduction to Pulping:History 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

PSE 476: Lecture #1


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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.

PSE 476: Lecture #1


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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)

PSE 476: Lecture #1


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Regional Affects on Raw Material

For this lecture,

we will be looking

at raw material use

by these regions.

PSE 476: Lecture #1


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Raw Material Log/Chip Makeup

PSE 476: Lecture #1


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Raw Material Log/Chip Makeup

PSE 476: Lecture #1


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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

PSE 476: Lecture #1


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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%)

  • 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 gr =

  • x 100%

Wet wood mass

Mass of water in wood

MC OD =

  • x 100%

Oven dry wood mass

PSE 476: Lecture #1


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Density =

Unit volume of green wood

Raw Material HandlingPhysical Measurements

  • 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

Dry weight of wood

PSE 476: Lecture #1


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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.

PSE 476: Lecture #1


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1/2 to 1” long

Variable

Width

TOP

Side

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

PSE 476: Lecture #1


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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.

PSE 476: Lecture #1


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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)

PSE 476: Lecture #1


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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 45-55°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.

PSE 476: Lecture #1


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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.

PSE 476: Lecture #1


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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).

PSE 476: Lecture #1


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