{"@context":{"@language":"en","Affiliation":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","AggregatedSourceRepository":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","Campus":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","Creator":"http:\/\/purl.org\/dc\/terms\/creator","DateAvailable":"http:\/\/purl.org\/dc\/terms\/issued","DateIssued":"http:\/\/purl.org\/dc\/terms\/issued","Degree":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","DegreeGrantor":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","Description":"http:\/\/purl.org\/dc\/terms\/description","DigitalResourceOriginalRecord":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","FullText":"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note","Genre":"http:\/\/www.europeana.eu\/schemas\/edm\/hasType","GraduationDate":"http:\/\/vivoweb.org\/ontology\/core#dateIssued","IsShownAt":"http:\/\/www.europeana.eu\/schemas\/edm\/isShownAt","Language":"http:\/\/purl.org\/dc\/terms\/language","Program":"https:\/\/open.library.ubc.ca\/terms#degreeDiscipline","Provider":"http:\/\/www.europeana.eu\/schemas\/edm\/provider","Publisher":"http:\/\/purl.org\/dc\/terms\/publisher","Rights":"http:\/\/purl.org\/dc\/terms\/rights","RightsURI":"https:\/\/open.library.ubc.ca\/terms#rightsURI","ScholarlyLevel":"https:\/\/open.library.ubc.ca\/terms#scholarLevel","Title":"http:\/\/purl.org\/dc\/terms\/title","Type":"http:\/\/purl.org\/dc\/terms\/type","URI":"https:\/\/open.library.ubc.ca\/terms#identifierURI","SortDate":"http:\/\/purl.org\/dc\/terms\/date"},"Affiliation":[{"@value":"Applied Science, Faculty of","@language":"en"},{"@value":"Chemical and Biological Engineering, Department of","@language":"en"}],"AggregatedSourceRepository":[{"@value":"DSpace","@language":"en"}],"Campus":[{"@value":"UBCV","@language":"en"}],"Creator":[{"@value":"Mohamad, Masita","@language":"en"}],"DateAvailable":[{"@value":"2013-02-28T00:00:00","@language":"en"}],"DateIssued":[{"@value":"2012","@language":"en"}],"Degree":[{"@value":"Master of Applied Science - MASc","@language":"en"}],"DegreeGrantor":[{"@value":"University of British Columbia","@language":"en"}],"Description":[{"@value":"Often, fibre fractionation produce a higher value long-fibred reject stream and a lower\nvalue short-fibred accept stream simultaneously. Fractionation is only practical when a\nmill can make use of all obtained fractions. This study sought to demonstrate the\npotential of upgrading the reject fraction through multiple stages of fractionation while\ncreating a new market for the remaining low value pulp for an efficient use of the raw\nmaterials.\nIn this study, an NBSK pulp was fractionated on the basis of fibre length using a small\nindustrial pressure screen Beloit MR-8 in multiple consecutive stages to isolate the lowvalue\nfines fraction from the feed pulp using the best combination of operating\nparameters. The best conditions to carry out fractionation were determined by conducting\nexperiments to investigate the effect of varying volumetric reject ratio, Rv aperture\nvelocity, Vs aperture diameter and rotor tip speed, Vt on reject thickening and passage\nratio using several smooth-holed screen cylinders. This work shows that in general,\nincreasing fines percentage in the accept and increasing fibre length in the reject were\nobtained by using the screen cylinder with 0.5 mm apertures, the highest Rv at 0.6 and the\nsmallest Vs at 0.3 ms-\u00b9.\nThe strength properties of the unfractionated pulp were compared to the reject pulp\nproduced from the multistage fractionation. The tensile strength of the final reject pulp\n(which is 95 wt-% of the feed pulp) was increased up to 40% through the removal of only\na small amount of fines. The TEA, burst and tear indexes also improved. The Gurley air\nresistance was decreased up to 50%.\nThe final accept fraction contains a significantly higher proportion of fines and it was\nanalyzed by FPInnovations for its potential suitability as a raw material for a novel fibre\nbased product, Nanocrystalline Cellulose (NCC).","@language":"en"}],"DigitalResourceOriginalRecord":[{"@value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/42993?expand=metadata","@language":"en"}],"FullText":[{"@value":" MULTISTAGE FIBRE LENGTH FRACTIONATION OF SOFTWOOD CHEMICAL PULP USING A PRESSURE SCREEN EQUIPPED WITH SMOOTH-HOLED SCREEN CYLINDER by Masita Mohamad B. Eng., Vanderbilt University, 2009 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied Science in The Faculty of Graduate Studies (Chemical and Biological Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2012 \u00a9 Masita Mohamad 2012 ii Abstract Often, fibre fractionation produce a higher value long-fibred reject stream and a lower value short-fibred accept stream simultaneously. Fractionation is only practical when a mill can make use of all obtained fractions. This study sought to demonstrate the potential of upgrading the reject fraction through multiple stages of fractionation while creating a new market for the remaining low value pulp for an efficient use of the raw materials. In this study, an NBSK pulp was fractionated on the basis of fibre length using a small industrial pressure screen Beloit MR-8 in multiple consecutive stages to isolate the low- value fines fraction from the feed pulp using the best combination of operating parameters. The best conditions to carry out fractionation were determined by conducting experiments to investigate the effect of varying volumetric reject ratio, Rv aperture velocity, Vs aperture diameter and rotor tip speed, Vt on reject thickening and passage ratio using several smooth-holed screen cylinders. This work shows that in general, increasing fines percentage in the accept and increasing fibre length in the reject were obtained by using the screen cylinder with 0.5 mm apertures, the highest Rv at 0.6 and the smallest Vs at 0.3 ms -1 . The strength properties of the unfractionated pulp were compared to the reject pulp produced from the multistage fractionation. The tensile strength of the final reject pulp (which is 95 wt-% of the feed pulp) was increased up to 40% through the removal of only a small amount of fines. The TEA, burst and tear indexes also improved. The Gurley air resistance was decreased up to 50%. The final accept fraction contains a significantly higher proportion of fines and it was analyzed by FPInnovations for its potential suitability as a raw material for a novel fibre based product, Nanocrystalline Cellulose (NCC). iii Table of Contents Abstract ............................................................................................................................... ii Table of Contents ............................................................................................................... iii List of Tables ...................................................................................................................... vi List of Figures ................................................................................................................... vii Nomenclature ..................................................................................................................... xi Acknowledgments ............................................................................................................. xii Dedication ........................................................................................................................ xiii 1 Introduction ................................................................................................................. 1 1.1 Background ........................................................................................................... 1 1.1.1 Wood and fibre structure ............................................................................... 1 1.1.2 Fibre fractionation in a pressure screen ......................................................... 6 1.1.3 Screening mechanism .................................................................................. 10 1.1.4 Screening theory .......................................................................................... 11 1.1.5 Pressure screen parameters .......................................................................... 16 1.2 Summary of the literature ................................................................................... 18 1.3 Objectives of the study ....................................................................................... 19 1.5 Structure of the thesis ......................................................................................... 20 2 Materials and methods .............................................................................................. 21 2.1 Feed pulp ............................................................................................................ 21 2.2 Pressure screen setup .......................................................................................... 22 2.3 Trial procedures .................................................................................................. 24 2.4 Pulp evaluations .................................................................................................. 26 3 Influence of pressure screen operating parameters on fractionation ......................... 29 3.1 Fibre passage ratio and reject thickening behaviour........................................... 30 3.1.1 Effect of screen cylinder aperture diameter ................................................ 30 3.1.2 Effect of aperture velocity ........................................................................... 34 3.1.3 Effect of volumetric reject ratio .................................................................. 35 3.2 Accept pulp quality ............................................................................................. 37 3.2.1 Length-weighted average fibre length ......................................................... 37 iv 3.2.2 Length-weighted fines percentage .............................................................. 38 3.3 Reject pulp quality .............................................................................................. 40 3.3.1 Length-weighted average fibre length ......................................................... 40 3.3.2 Length-weighted fines percentage .............................................................. 41 4 First stage of fractionation ......................................................................................... 42 4.2 Screening conditions and their effects on fractionation ..................................... 42 4.1.1 Freeness change ........................................................................................... 44 4.2 Fibre length distribution changes ....................................................................... 45 4.3 Qualitative differences of resulting fractions ..................................................... 46 5 Rejects fractionation stages ....................................................................................... 48 5.1 Effect of changing operating parameters at second-stage .................................. 49 5.1.1 Effect of volumetric reject ratio and aperture velocity ............................... 49 5.1.2 Effect of rotor tip speed ............................................................................... 50 5.2 Screening conditions and their effects on fractionation ..................................... 51 5.3 Fibre length distribution changes ....................................................................... 52 5.4 Qualitative differences of rejects R1 and R2 ...................................................... 53 5.4.1 Microscope images ...................................................................................... 53 5.4.2 Handsheet analyses ..................................................................................... 55 5.3 Fibre passage ratio at second stage ..................................................................... 57 5.4 Fractionation efficiency ...................................................................................... 59 5.4.2 Mass balance around a pressure screen ....................................................... 59 5.4.3 Coarseness versus length relationship, \u03c9(l) ................................................ 60 5.4.4 Enrichment of long fibres in the reject streams ........................................... 61 6 Accepts fractionation stages ...................................................................................... 63 6.1 Effect of operating parameters at second-stage .................................................. 64 6.1.1 Effect of volumetric reject ratio .................................................................. 64 6.1.2 Effect of rotor tip speed ............................................................................... 64 6.2 Screening conditions and their effects on fractionation ..................................... 65 6.3 Fibre length distribution changes ....................................................................... 66 6.4 Qualitative differences of accepts A1 and A2 .................................................... 67 6.5 Fibre passage ratio at second stage ..................................................................... 69 v 6.6 Enrichment of fines in the accept streams .......................................................... 69 6.7 Fines fraction for NCC production ..................................................................... 71 7 Conclusion ................................................................................................................. 72 7.1 Recommendations for future work ..................................................................... 73 References ......................................................................................................................... 74 Appendices ........................................................................................................................ 77 Appendix A: Multi-stage fractionation system layout ............................................... 77 Appendix B: Fibre length fractionation in a Bauer-McNett classifier ...................... 78 Appendix C: Coarseness versus length relationship, \u03c9(l) ......................................... 80 vi List of Tables Table 1. Classes of parameters. ..................................................................................... 16 Table 2. NBSK pulp fibre morphological properties .................................................... 21 Table 3. Summary of screen design and operating parameters used during the first stage of fractionation (total of 28 screening tests) .......................................... 25 Table 4. Tested handsheet properties and relevant TAPPI test methods used in this study. ............................................................................................................... 28 Table 5. Combination of operating parameters that were tested using three different screen cylinders at the first stage of fractionation. .......................................... 29 Table 6. Optimum screening conditions for the first stage of fractionation. Fractionation results are presented in length-weighted (LW) averages. ............................... 43 Table 7. Screening conditions for the reject fractionation series and the fractionation results at each stage. ........................................................................................ 51 Table 8. Handsheet properties of feed, reject R1 and R2 fractions. Percent changes of the final R2 properties with respect to the properties of handsheets made from the original pulp are shown. ............................................................................ 55 Table 9. Mass percent of fibres in feed and reject streams calculated using estimated \u03c9i. ..................................................................................................................... 62 Table 10. Screening conditions for the accept fractionation series. ................................ 65 vii List of Figures Figure 1. Microscopic structures (transverse view) of (a) spruce (softwood) and (b) birch species (hardwood). (V) shows vessel elements. Handbook For Pulp & Paper Technologists, 2002, by permission. ............................................... 2 Figure 2. Illustration of a tracheid structure. ML is the middle lamella, P is the primary wall, S is the secondary wall and L is the lumen. Handbook For Pulp & Paper Technologists, 2002, by permission. ...................................... 2 Figure 3. Length-weighted fibre length distributions of chemical softwood and chemical hardwood pulps .............................................................................. 3 Figure 4. Light microscope image of NBSK pulp (mixture of spruce, pine and fir fibres). NBSK fibre collapses readily into a ribbon-like structure. Length- weighted average fibre length is about 2.5 mm............................................. 5 Figure 5. A modern industrial pressure screen. Handbook of Pulp, 2006, by permission. .................................................................................................... 6 Figure 6. Schematic of an axially fed pressure screen with a two-foil rotor and the velocity components near the screen cylinder. .............................................. 8 Figure 7. Smooth-holed screen cylinders with several aperture sizes (1.0 mm, 0.8 mm and 0.5 mm) used in this study. ..................................................................... 8 Figure 8. Types of screening. (a) shows barrier screening and (b) shows probability screening. ..................................................................................................... 10 Figure 9. Flows and consistencies around an annular differential volume element. Adapted from [20]. ...................................................................................... 12 Figure 10. Reject thickening behaviour as predicted by the plug flow model. 0