Chip Screening, Contaminants Removal and Overs and Overthick - PowerPoint PPT Presentation

Chip Screening, Contaminants Removal and Overs and Overthick Treatment Jun Tian Chief Engineer VP Engineering Acrowood Corporation www.Acrowood.com Everett, WA 88203 USA January 14, 2017

Wood Chips Categories

Why do we screen chips? When pulping wood chips (especially by the “Kraft” process) size is very important. Effect of Chip Size on Kraft Pulp Yield Effect of Chip Size on Kraft Pulp Yield Effect of Chip Size on Bleachable Grade Kraft Pulp Rejects Effect of Chip Size on Bleachable Grade Kraft Pulp Rejects 50 50 Replicate Replicate Brownstock Screened Yield, wt% Brownstock Screened Yield, wt% Average Average 50 50 Brownstock Rejects (0.010" cut), wt% Brownstock Rejects (0.010" cut), wt% 45 45 Replicate Replicate Bigger, Thicker Chips Bigger, Thicker Chips Average Average 40 40 40 40 35 35 30 30 30 30 20 20 25 25 Bigger, Thicker Chips Bigger, Thicker Chips 10 10 20 20 -4,+2 mmt -4,+2 mmt -6,+4 mmt -6,+4 mmt -8,+6 mmt -8,+6 mmt -10,+8 mmt -10,+8 mmt -12,+10 mmt -12,+10 mmt +12 mmt +12 mmt -3/16"r -3/16"r -2 mm,+3/16"r -2 mm,+3/16"r 0 0 -3/16"r -3/16"r mm,+3/16"r mm,+3/16"r -4,+2 mmt -4,+2 mmt -6,+4 mmt -6,+4 mmt -8,+6 mmt -8,+6 mmt -10,+8 mmt -10,+8 mmt -12,+10 mmt -12,+10 mmt +12 mmt +12 mmt -2 -2 Chip Size Categories Chip Size Categories Chip Size Categories Chip Size Categories Small wood particles do NOT dissolve !! 1% yield change = 5-10,000,000 $/Y change in mill revenue

Chip Size Distribution Example of a classification method: ChipClass™ Retained Hole chips are: size/type: Overlong 45 mm round hole Overthick 8 mm slots 7 mm round hole Accepts 3 mm round hole Pin chips Fines

Chip Size Distribution Too big and Too small chips and Issues: Too big: Too small: 1. Oversize / Overlong : 3. Pin chips : physical handling liquor circulation problems problems 2. Overthick : 4. Fines : pulping chemical lower yield, higher penetration problems, dirt and bark, lower yield loss, knotter strength pulp rejects, shives (shorter pulp fiber length)

Generic Screening Processes Gross Overs Chip Thickness Scalper and Fines Screening OR Oversize Reduction Chips Overthick Thickness Screen Chip Rotary Cleaning Oversize to Screen Rocks Rechipper Overthick Treatment Fines “Good” Fines Chips Screen Fines Good Chips to Digester Typically, sawmill or chip plant application Typically, pulpmill application

Screening for Gross Oversize Disk Scalpers, Scalping Screens

Screening for Gross Oversize Gyratory screens (a.k.a. Rotary or Shaker) Generally do fines removal also Hole sizes / shapes Oversize : 1.5 to 3 inches Fines : 1/8 to 1/2 inch

Rechipping of Gross Oversize Many types of rechippers used  Generally, results are not all that great  Examples: Type %>10mm thick -7,+3mm Pins -3mm Fines Disk 10-35% 5-23% 1-8% Drum 0-18% 9-33% 2-8% Hogs 5-30% 17-40% 3-10%

Screening for Overthick Gyratory Screens Sizes range from 4 to 14 feet  wide by 6 to 24 feet long Screens sloped 7 to 15 degrees  From 2 to 5 inch circular motion  Rotation speed from 180 to 300  RPM Can alter hole size inexpensively  to alter performance Deck materials can be mild or  stainless steel, to resist wear and corrosion

Screening for Overthick Gyratory Screens  Thickness separation based on typically strong correlation between chip length, width and thickness for large chips  Perform by stratifying chips into sizes  Can get high removal efficiency, but generally high carry-over; I.E., Not real high performance index  Relatively inexpensive to obtain and maintain compared to other ‘true’ thickness screens

Screening for Overthick Disk Screens Parallel shafts with intermeshed disks, all rotating in  the same direction Space between disks (Inter-Facial Opening, or IFO)  screens for chip thickness Overthick Chips IFO Accepts

Screening for Overthick "Flat" Disk Screens Single-sized disk or alternating diameter disc pattern  All shafts on one level, or “Raised-roll” configuration 

Screening for Overthick Roll Thickness Screen High performance  index No expensive  disk assemblies Easier to maintain  slot opening precision Adjustable IRO  Fully chromed  surface

Roll Screen vs. Bar Screen The DiamondRoll VIRO Thickness Screen has very accurate slot openings, which remain accurate after years of operation. Bar screen misalignment requires regular adjustment.

Overthick Chip Reduction Slicers Very efficient overthick reduction with some fines and pins generation  2 drums rotating same direction at different speeds  outer knife ring • • inner anvil or paddle ring rotates faster, pushes overthick chips through 6 to 7.5 mm knife gap Overthick Anvil Ring Chip (or s Rotor) ~ 350 RPM ~ 150 RPM Sliced Chips Knife Ring

vs. “Re-chipping” How Slicing Works

Overthick Chip Reduction Crackers and Conditioners  Fissures overthick chips to allow liquor penetration  No knives to change, or anvils to keep sharp  Low fines and pins generation

Cracked Chips

Screening for Fines Roll Fines Screen Rolls with targeted diamond knurled pattern  Inter-roll spacing distance 0.5 to 3 mm  Variable speed to significantly alter fines removal and accept fiber loss  Used as secondary fines screen, and for pins recovery screen 

Roll Fines Screen • Separates fines and pins from acceptable chips • Fines and pins sections possible for independent pins control • Possible combination with Roll Thickness Screen • Field adjustable for IRO and roll speed • Works well in icy cold conditions

Chip Cleaning Removal of Metal, Stones, Sand, Grit, etc. Non-ferrous metal removal: Eddy current separator  • Need separate removal device Magnets for ferrous metal removal 

Chip Cleaning Chip Washers Rock removal for overthick chip treatment protection  Sand and grit removal - often used in mechanical pulping  Water issues – re-use requires treatment, high BOD as effluent, increase in  moisture content

Air Density Separator System • Separation zone • Piping • Cyclone and Vortex Breaker • Discharge airlock • Fan and controls • Silencer

Chip Cleaning Air Density Separators Rock removal for overthick chip treatment protection  Will remove some dense wood - knots  Quite efficient at removing dense tramp material  Noisy, and require a lot of power for fan 

ADS Rejects Are More Than Rocks • Knots, • Knots, • Air flow is adjustable compression compression to control the size and wood, mud, wood, mud, quality that is removed ice lumps ice lumps • Measure air flow in • Few good • Few good the separation zone wood pieces wood pieces for best control

Screening for Overthick and Fines General Elements Feed Overthick Contaminant Removal Screening Overthick Fines Screening Reduction Accepts

Screening for Overthick and Fines System Alternatives Flat Disk, etc. -> Gyratory Feed Flat Disk Screen Overthick Contaminant Removal Accepts & Fines Overthick Gyratory Screen Reduction Fines Accepts

Screening for Overthick and Fines System Alternatives Gyratory only Feed Gyratory Screen Overthick & Accepts Contaminant Removal Fines Overthick Reduction Accepts

Summary : Why We Screen Chips Chip Size Distribution - Before Screening 2 4 6 8 10 Relative Amount Source B 2 4 6 8 10 2 4 6 8 10 Source A Accepts Source B Source B % Overthick Source A Source A % Overthick % Overthick Source C Fines Pins Overthick Chip Size Source C Source C Chip Size Distribution - After Screening System Performance Target System Performance Target System Performance Target Relative Amount Accepts 1 2 3 1 2 3 4 1 2 3 4 % Fines % Fines % Fines Fines Pins Overthick Chip Size