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The importance of fibre flocculation in flotation deinking P. Huber #, E. Zeno #, B. Fabry #, X. Rousset #, M.C. Angelier #, D. Beneventi*, T. Vazhure.

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Presentation on theme: "The importance of fibre flocculation in flotation deinking P. Huber #, E. Zeno #, B. Fabry #, X. Rousset #, M.C. Angelier #, D. Beneventi*, T. Vazhure."— Presentation transcript:

1 The importance of fibre flocculation in flotation deinking P. Huber #, E. Zeno #, B. Fabry #, X. Rousset #, M.C. Angelier #, D. Beneventi*, T. Vazhure & # :CTP, *: LGP2, & : Aylesford Newsprint COST FP1005 “Fibre suspension flow modeling” Oct. 2012, Trondheim, Norway

2 2 COST FP1005 – Trondheim oct 2012 Background Influence of pulp concentration on flotation efficiency (laboratory flotation) Yu, C.J. (1994), TAPPI Recycling Symposium Proceedings: ,  The higher the concentration, the lower the ink removal Surprisingly, very little information is available concerning the effect of total concentration on flotation efficiency (let alone fibre concentration) Li, R. et al., (2006).. Research progress in pulping and papermaking. Guangzhou, China, pp

3 3 COST FP1005 – Trondheim oct 2012 Influence of pulp concentration on flotation efficiency (pilot flotation trials – VOITH facility) Britz, H., Peschl, A. (1994), Wochenblatt für Papierfabrikation, n°15: , Accepts brightness concentration conc. flot. cell # Tot. (%)Fibres (%) Losses (%) Concentration (%) At same brightnessAt same cleanliness  The higher the concentration, the lower the ink removal and the better the yield Background

4 4 COST FP1005 – Trondheim oct 2012 Background Influence of concentration on air content (industrial flotation trials) Dorris, G.M., Pagé, N., Gendron, S., Murray, T. & Ben, Y. (2006) Prog. Pap. Recycling, 16 (1), pp  The higher the concentration, the lower the air content  The higher the air content, the better the ink removal Air content Ink removal

5 5 COST FP1005 – Trondheim oct 2012 Mechanisms Hypothesis (Dorris et al. 2006) High concentration  (flocculation ?)  heterogeneous fibre suspension  chanelling  air bubbles can travel faster, coalescence and rise faster to the top of the cell  Decrease of relative residence time air/pulp  air content is reduced  ink removal is impaired

6 6 COST FP1005 – Trondheim oct 2012 Background Influence of concentration on fibre flocculation (laboratory trials with various pulps) Huber, P., Carré, B., and Petit-Conil, M. (2008). BioRes. 3(4),  The higher the concentration, the higher the fibre flocculation Example with TMP fibres Same results with BKP (HW, SW, mix), DIP, etc.

7 7 COST FP1005 – Trondheim oct 2012 Background Influence of crowding factor on pulp flocculation (flocculation varied by changing concentration and pulp mixtures HW/SW) Huber P., Roux J.C., Mauret E., Belgacem N., and Pierre C. (2003), J. Pulp & Pap. Sci. 29(3):  fibre crowding determines fibre flocculation (at given turbulence)

8 8 COST FP1005 – Trondheim oct 2012 Background Influence of crowding factor on gas hold-up (Column bubbling of virgin pulp) Tang, C. & Heindel, T.J. (2006) The Canadian Journal of Chemical Engineering, 84 (2), pp  The higher the fibre crowding, the lower the air content Gas hold-up (crowding)

9 9 COST FP1005 – Trondheim oct 2012 Motivations & objectives influence of pulp flocculation on flotation efficiency ? How to vary flocculation ? By changing concentration By adding dispersants Non surface-active fibre dispersants : Guar gum CMC

10 10 COST FP1005 – Trondheim oct 2012 Outline Background Methods : flocculation sensor, gas hold-up sensor… Results Effect of concentration Effect of dispersants Mechanisms

11 11 COST FP1005 – Trondheim oct 2012 Assessment of fibre flocculation General methods Pulp circulation on the flocculation pilot loop Fibre flocculation testing with the CTP FlocSens (image analysis) Constant flow speed : equivalent shear rate = 690 s -1 (medium speed) Flocculation sensor (+overflow) installed on Recycled fibres pilot plant, at flotation inlet Materials and Methods Flocculation measurement

12 12 COST FP1005 – Trondheim oct 2012 Flocculation sensor principles Flocculation index : binary morphology  floc size distribution Flocculation index: SiSi DiDi diameter surface …

13 13 COST FP1005 – Trondheim oct 2012 Reduced sensitivity to light diffusion Problem : filler diffuse light Even in presence of light diffusing filler :  Fibre flocculation measurement is possible (independently on filler flocculation level) Huber P., Roux J.C., Mauret E. and Carré B. (2006), APPITA Journal 59(1):37-43 (no filler) Fibres onlyFibres+20% filler RMS = FI = 2.63 mm² RMS = FI = 2.65 mm²

14 14 COST FP1005 – Trondheim oct 2012 Flotation monitoring : Assessment of pulp aeration Air content ≠ Air ratio Air ratio is a mechanical parameter only Air content is a true measurement of pulp aeration Includes both hydraulic and physico-chemical effects  relevant parameter that affects flotation efficiency  S b is proportional to air content Leichtle (1998) flotation rate constant collection efficiency bubble surface area flux

15 15 COST FP1005 – Trondheim oct 2012 Flotation monitoring : On-line measurement of air content Paprican sensor Based on pressure difference between immersed gauges Apparent pulp density varies with air content Installation Installed on reject side, across the hatch, at an angle of 60° probes installed in pre-flotation 1 ry Dorris et al. (2006) PP

16 16 COST FP1005 – Trondheim oct 2012 Materials & methods : CTP pilot plant Pilot Trial Additive addition (if any) i) Flocculation measurement ii) Bubble size measurement iii) Air content measurement iv) Sampling for CFC sampling

17 17 COST FP1005 – Trondheim oct 2012 Materials & methods Pilot Trial: materials (metering pump before flotation inlet, contact time = 30 s) Pulp concentration = 12 g/L

18 18 COST FP1005 – Trondheim oct 2012 Pilot verticell Materials and Methods Bubble collection via a sampling pipe and visualization in a glass window Automated bubble count using a CCD camera and image analysis software (Sherlock 7) ii) Bubble size measurement Halogen light source CCD camera Viewing chamber PC for image analysis Bubble size distribution D.Beneventi,

19 19 COST FP1005 – Trondheim oct 2012 Flocculation Effect of concentration Effect on fibre flocculation (flotation cell inlet) 8 g/L16 g/L Fibre fraction = 56% Pulp flocculation increases when increasing pulp concentration (8-16 g/L) Higher crowding More fibres interacting with each other (mainly governed by fibre concentration)  stronger flocculation

20 20 COST FP1005 – Trondheim oct 2012 Effect of concentration : lab trials Results Lab flotation (Voith cell) concentration from 8 to 14 g/L Higher concentration Impairs ink removal reduces total, ash losses, fibres and fines losses variation of concentration leads to a unique selectivity trend (ink removal vs. Losses) 1 pt of ink removal gain will cause –constant yield losses penalty (pt) –constant ash losses penalty (pt) Selectivity index (ink removal/losses) slightly better at higher concentration concentration (10% ink removal causes 10% ash losses)

21 21 COST FP1005 – Trondheim oct 2012 The higher the concentration  the higher the pulp flocculation Higher concentration causes : Lower ink removal However effect more pronounced when total conc.>12g/L (or fibre concentration >6.7 g/L) Higher total losses but lower ash losses but much higher fibre content in froth (because of low froth height)  Little impact on ash flotation selectivity concentration Effect of concentration : pilot trials

22 22 COST FP1005 – Trondheim oct 2012 Effect of concentration: industrial trials at Aylesford Air content Large variations of air content over time (in 1ry) Higher air content contributes to better ink removal efficiency Higher air impairs flotation yield Higher air content is caused by concentration decrease  To maximise the flotation yield, work at highest possible concentration while maintaining ERIC target (But take care, it is a question of compromise: a too high consistency will induce a too high decrease in ink removal efficiency) Huber, P., Rousset, X., Zeno, E. and Vazhure, T. (2011) Ind. Eng. Chem. Res. 50(7) :

23 23 COST FP1005 – Trondheim oct 2012 On the fibre flocculation Selected dispersants (Guar gum and CMC) effectively de- flocculate DIP -14 to 19 % reference +1% guar+2% guar +1% CMC+2% CMC Flocculation Effect of dispersants (Flotation cell inlet)

24 24 COST FP1005 – Trondheim oct 2012 Effect of dispersants : lab trials Effect of CMC at flotation CMC behaviour at flotation Limited but fast adsorption on solid material No effect on surface tension Follows water flows, no selective separation Clear selectivity increase (for total, ash, fibre losses) long flotation time  significant reduction of losses at comparable ink removal short flotation time  reduction of losses AND ink removal increase Slight selectivity decrease for fines losses (?)

25 25 COST FP1005 – Trondheim oct 2012 Effect of dispersants : pilot trials Selected dispersants (guar gum or CMC) clearly improved flotation selectivity  Better ink removal + lower losses at the same time Zeno, E., Huber, P., Rousset, X., Fabry, B. and Beneventi D. (2010). Ind. Eng. Chem. Res., 2010, 49 (19), pp 9322–9329 Increased air content thanks to pulp de-flocculation (at the fibre level) Lower entrainment of fine elements thanks to depressing mechanism (from adsorbed dispersants) (high overall losses because of low froth height)

26 26 COST FP1005 – Trondheim oct 2012 Better selectivity : the link is fibre flocculation flocculation directly influenced the pulp aeration : Gas hold-up  when flocculation  Effect of dispersants : pilot trials Zeno, E., Huber, P., Rousset, X., Fabry, B. and Beneventi D. (2010). Ind. Eng. Chem. Res., 2010, 49 (19), pp 9322–9329

27 27 COST FP1005 – Trondheim oct 2012 Bubble size ? Effect of dispersants : pilot trials Drift flux model : Rising velocity in Newtonian fluid : Limited bubble size decrease  Not sufficient to explain increased gas hold-up  Higher drag on bubbles in de-flocculated pulp Zeno, E., Huber, P., Rousset, X., Fabry, B. and Beneventi D. (2010). Ind. Eng. Chem. Res., 2010, 49 (19), pp 9322–9329

28 28 COST FP1005 – Trondheim oct 2012 Mechanisms Improved mechanism (this work) Lower (fibre) concentration or add fibre dispersants  de-flocculation  homogeneous fibre suspension  higher drag on air bubbles  rise slowly to the top of the cell  increase of relative residence time air/pulp  air content is increased  ink removal is improved (limited coalescence (surfactants)  limited chanelling)

29 29 COST FP1005 – Trondheim oct 2012 Conclusions Relationship among flocculation, ink removal, turbulence and air content is not simple Depends on hydraulic regimes in the flotation cells (turbulence pattern) (lab cell ≠ pilot cell ≠ industrial cell ≠ various industrial flotation cells config.) Will affect interactions between air bubbles and pulp flocs Pulp flocculation does impact flotation efficiency Mechanisms involved Ink removal : –pulp de-flocculation (at fibre level)  homogeneous fibre network higher  higher drag  higher air content  better ink removal Losses : –With concentration : mechanism not clear –With dispersants : Lower entrainment of fine elements thanks to depressing mechanism (from adsorbed dispersants) Selectivity ? When increasing concentration : poorer ink removal, lower losses But little impact on selectivity With added dispersants : clear selectivity increase (at least at lab and pilot scale)


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