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

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Presentation on theme: "PSE 476: Lecture #11 Pulping and Bleaching PSE 476 Lecture #1 Introduction Lecture #1 Introduction."— Presentation transcript:

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

2 PSE 476: Lecture #12 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

3 PSE 476: Lecture #13 Papyrus Making-Harvesting

4 PSE 476: Lecture #14 Papyrus Making-Peeling

5 PSE 476: Lecture #15 Papyrus Making-Cutting

6 PSE 476: Lecture #16 Papyrus Making-Soaking

7 PSE 476: Lecture #17 Papyrus Making-Rolling

8 PSE 476: Lecture #18 Papyrus Making-Pressing, Drying

9 PSE 476: Lecture #19 Papyrus Making-Final Product

10 PSE 476: Lecture #110 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) 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)

11 PSE 476: Lecture #111 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 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

12 PSE 476: Lecture #112 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.

13 PSE 476: Lecture #113 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)

14 PSE 476: Lecture #114 Regional Affects on Raw Material For this lecture, we will be looking at raw material use by these regions.

15 PSE 476: Lecture #115 Raw Material Log/Chip Makeup

16 PSE 476: Lecture #116 Raw Material Log/Chip Makeup

17 PSE 476: Lecture #117 Raw Material Handling Physical 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

18 PSE 476: Lecture #118 Raw Material Handling Physical Measurements Moisture Content - Green (paper industry) »Wet basis, amount of water in wood as a fraction of wet weight of wood »Typical MC gr 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 MC gr 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 MC OD of freshly cut wood = 100% (45-150%) Mass of water in wood Oven dry wood mass MC OD = x 100%

19 PSE 476: Lecture #119 Raw Material Handling Physical 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/ft 3 or kg/m 3 Dry weight of wood Density = Unit volume of green wood

20 PSE 476: Lecture #120 Raw Material Handling Debarking 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.

21 PSE 476: Lecture #121 Raw Material Handling Chip 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 Variable Width Side 1/8 to 1/4” thick

22 PSE 476: Lecture #122 Raw Material Handling Wood Deterioration Wood decay requires moisture and oxygen. »Moisture content > 20% MC OD. »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% MC OD would slow degradation. -Economically unsound. -Would slow liquor penetration and therefore pulping. Wood decay requires moisture and oxygen. »Moisture content > 20% MC OD. »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% MC OD would slow degradation. -Economically unsound. -Would slow liquor penetration and therefore pulping.

23 PSE 476: Lecture #123 Raw Material Handling Chip 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)

24 PSE 476: Lecture #124 Raw Material Handling Deterioration 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.

25 PSE 476: Lecture #125 Raw Material Handling Debris 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.

26 PSE 476: Lecture #126 Raw Material Handling Screening 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).


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