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High-speed dispersing between two deinking loops: are there optimisation possibilities? Benjamin FABRY and Bruno CARRE Niagara Falls, September 2007 Guideline Introduction Theoretical aspects High-speed dispersing between two

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High-speed dispersing between two deinking loops: are there optimisation possibilities?

Benjamin FABRY and Bruno CARRE Niagara Falls, September 2007

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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Introduction Generality

  • Hot-dispersion in deinking plant has started to be used

since 1976

  • Mechanical treatment at high temperature and high

consistency with the use of appropriate techniques to transfer energy to pulp

  • Main applications:
  • Dispersion of contaminants (hot-melts, stickies, specks…)
  • Ink detachment prior to post-deinking
  • Bleaching
  • Microbiological decontamination
  • Changes in fibre properties
  • Since the end of the 80's, dispersion becomes a basic

treatment in multi-loop deinking processes

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Introduction Objectives

  • To determine the incidence of dispersing parameters
  • n
  • Ink detachment and final optical properties (ink removal,

brightness and cleanliness)

  • Morphological fibre characteristics
  • i.e., to determine the best conditions allowing
  • To obtain the best deinked pulp properties
  • To obtain the lowest drawbacks
  • Associated with the lowest energy consumption and the

lowest cost

  • Through a systematic study where a new, easy and

useful method will be presented

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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Theoretical aspects Generality

  • The easiest way to characterize mechanical treatment

is to consider the specific energy consumption (kWh/T)

  • Advantage: Directly economic consideration
  • Drawbacks: No phenomena characterization
  • Since few years, more fundamental approaches have

been proposed (transfer from refining theory)

  • Brecht approach

With the specific edge load (SEL) and effective power input per total edge length per second (Lb)

  • Miles and May approach:

Distinction between the number of bar impacts (n) and specific energy per impact (e)

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Theoretical aspects Generality

  • Since few years, more fundamental approaches have

been proposed (transfer from refining theory) – Rusinsky

et al.

  • Brecht approach:

Specific edge load (SEL) defined as the effective power input per total edge length per second (LB) Ink detachment occurs at the edges of dispersing elements Magnitude of the force applied at the edge of dispersing elements is the critical factor

  • Miles and May approach:

Distinction between the number of bar impacts (n) and specific energy per impact (e) Ink detachment is maximized at high e Ink redeposition is reduced at low n

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Theoretical aspects Generality

  • In the same period, CTP investigated dispersing

through fragmentation approach:

  • The different phenomena occurring during dispersing can be

viewed as 'solid' fragmentation described by two parameters

The forces involved: the overall forces can be described by energy consideration (volume energy consumption) even if we are not able to determine the specific energy applied to solid particles The 'solid' particle strength: function of particles considered (ink/fibre interactions, ink/ink interactions) and external parameters such as temperature, physico-chemical parameters

  • This concept has been successfully applied to have an
  • verall and composite information on pulping phenomena

(overall approach for LC, HC and drum pulpers)

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Theoretical aspect Fragmentation approach

  • Dispersing can be classified as fragmentation

Dispersing No fragmentation if the mechanical force is less intense than the resistive strength of the particles considered Fragmentation if the mechanical force is intense enough compared to the resistive strength of the particles considered

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Theoretical aspects Application of Volume Energy (Ev)

  • Volume energy consumption can be estimated by the

product between mass consistency (Cm) and specific energy consumption (Em)

  • Characterization of dispersing unit

implemented just after pulping stage

  • Low-speed kneader
  • High-speed disperser
  • Cm between 2.2 and 33%
  • Specific energy up to 210 kWh/T
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Theoretical aspects Application of Volume Energy (Ev)

  • No overall approach of ink fragmentation by

considering specific energy consumption

500 1000 1500 2000 2500 50 100 150 200 ERIC on entire pulp (ppm)

Low Consistency Medium Consistency High Consistency Medium Consistency High Consistency

High-speed Dispersing Low-speed Kneading Specific energy consumption (kWh/T)

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500 1000 1500 2000 2500 20 40 60 80 100 ERIC on entire pulp (ppm)

Low Consistency Medium Consistency High Consistency Medium Consistency High Consistency

High-speed Dispersing Low-speed Kneading

Estimated volume energy (Cm.Em)

Theoretical aspects Application of Volume Energy (Ev)

  • Possible to obtain a characteristic curve by

considering volume energy whatever the dispersing unit

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500 1000 1500 2000 2500 3000 1000 2000 3000 Calculated data Experimental data Ink fragmentation modelling through volume energy approach ERICentire pulp = 2100 - 750.e-0.0642.Cm.Em r² = 0.88

ERICentire pulp in ppm Cm : mass consistency expressed as fraction (-) Em : specific energy consumption (kWh/T)

Theoretical aspects Application of Volume Energy (Ev)

  • 1st order kinetic can describe ink fragmentation

ERICentire pulp = 2100 – 750.e-0.0642 Cm.Em

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100 200 300 400 20 40 60 80 100 ERIC on hyperwashed pulp (ppm) Low Consistency Medium Consistency High Consistency High-speed Dispersing Estimated volume energy Cm.Em (kWh/m3) Ink detachment and ink redeposition

Theoretical aspects Application of Volume Energy (Ev)

  • Ink detachment/redeposition can be described by

estimated volume energy

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Theoretical aspects Application of Volume Energy (Ev)

  • Volume energy consumption can be estimated by the

product between mass consistency (Cm) and specific energy consumption (Em)

  • It can describe phenomena involved during dispersing

such as for example ink fragmentation, ink detachment

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⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⋅ − ⋅ =

1 2 1 2 2 t r

r r r r w 2 c E a h N µ µ n ln ) ( ⋅ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − ⋅ =

1 2 1 2 2 r t

r r c a h N r r w 2 µ µ e ln ) (

µr : radial coefficient of friction µt : tangential coefficient of friction N : Average number of bar per unit length of arc h : number of rotating disk a : constant of friction c : pulp mass concentration r2 : outer radius dispersing zone r1 : inner radius dispersing zone w : rotational speed

Methodology Miles and May (1990, 1991)

  • Refining (and dispersing) can be characterized by
  • The number of impact imparted to a fibre (n)
  • The specific energy per bar impact imposed during refining

(e)

  • E = n . e

E: specific energy consumption in J/kg

Ec can be viewed as an approximation of volume energy Other parameters are constant in the present study

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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  • Pulping conditions
  • Drum pulper

Cm = 18% at 50°C – 25 min 0.7% NaOH, 0.7% soap, 2% silicate, 0.7% peroxide

  • Drum coarse screening

Holes: Ø 6 mm

  • Recovered papers (heated at 60°C during 3 days, i.e.,

condition responsible for poor ink detachment, high speck content, high ink fragmentation and poor ink removal)

  • 60% ONP (coldset offset)
  • 40% OMG

9.3% Heatset offset on LWC, 18.7% Heatset offset on SC, 7% rotogravure on LWC, 7% rotogravure on SC

Raw material and process parameters

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Fine screening Kadant Lamort CH3 // 20/100 Pilot flotation

steam steam Steam + chemical

1% NaOH 2.5% Silicate 1% Peroxide

MC thickening in vacuum filter HC thickening in screw press

Raw material and process parameters

For each dispersing treatment, several specific energies are applied

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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Thickening Steam

No effect No effect

Bleaching action without mechanical forces

No effect on ink Bleaching action Yield improvement

Softening of fibres Chemical

Increase in kink Increase in curl Increase in kink Increase in curl

Mechanical degradation (screw press) Effect On deinking On fibre

Increase in kink

Effect of thickening, steam and chemical Summary of the effects

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Incidence of thickening, steam and peroxide bleaching

chemicals

  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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40 50 60 70 80 20 40 60 80 °SR

MC dispersing HC dispersing HC dispersing + P chemicals

Estimated volume energy Em.Cm (kWh/m3)

Incidence of high- speed dispersing

  • n freeness

Dispersing between two deinking loops Incidence on fibre characteristics

  • Characteristic curve whatever the dispersing parameters
  • The higher the Ev, the higher the freeness (°SR)
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0.7 0.8 0.9 1.0 1.1 1.2 60 65 70 75 80 Mean fibre length (mm) 15 18 21 24 27 30 Fine content (based on area) %

MC dispersing HC dispersing HC dispersing + P chemicals

°SR

Full symbol fibre length Empty symbol Fine content

Dispersing between two deinking loops Incidence on fibre characteristics

  • Characteristic curve whatever the dispersing parameters
  • An increase in °SR (and in Ev) is responsible for fibre

cutting

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0.7 0.8 0.9 1.0 1.1 1.2 60 65 70 75 80 Mean fibre length (mm) 15 18 21 24 27 30 Fine content (based on area) %

MC dispersing HC dispersing HC dispersing + P chemicals

°SR

Full symbol fibre length Empty symbol Fine content

Dispersing between two deinking loops Incidence on fibre characteristics

  • Characteristic curve whatever the dispersing parameters
  • An increase in °SR (and in Ev) is responsible for fine

generation (and possible increase in losses)

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0.7 0.8 0.9 1.0 1.1 1.2 60 65 70 75 80 Mean fibre length (mm) 15 18 21 24 27 30 Fine content (based on area) %

MC dispersing HC dispersing HC dispersing + P chemicals

°SR

Full symbol fibre length Empty symbol Fine content

conventional Em range

Dispersing between two deinking loops Incidence on fibre characteristics

  • Note that no significant effect for conventional specific

energy application

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0.6 0.7 0.8 0.9 1.0 1.1 60 65 70 75 80 Relative fibre curl (-)

MC dispersing HC dispersing HC dispersing + P chemicals

°SR

Curl development during dispersing treatment

conventional Em range

Dispersing between two deinking loops Incidence on fibre characteristics

  • Without P bleaching liquor, no change in fibre curl
  • With P bleaching liquor, an increase in mechanical

treatment intensity is responsible for a decrease in Curl

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7.0 7.5 8.0 8.5 9.0 60 65 70 75 80 Fibre curl (%)

MC dispersing HC dispersing HC dispersing + P chemicals

°SR

Absolute fibre curl (pre-treatment + dispersing)

Dispersing between two deinking loops Incidence on fibre characteristics

  • Fibre curl is also function of pre-treatment (intensity of

thickening + introduction of P bleaching liquor)

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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50 100 150 200 250 20 40 60 80 ERIC on hyperwashed pulp (ppm) 50 54 58 62 66 70 Brightness on fibre fraction (% ISO)

MC dispersing HC dispersing HC dispersing + P chemicals

Estimated volume energy Cm.Em (kWh/m3)

Empty symbol brightness Full symbol ERIC

Dispersing between two deinking loops Incidence on optical properties

  • Characteristic curve whatever the dispersing parameters
  • The higher the Ev, the better the ink detachment
  • But a plateau is reached for Ev>10 kWh/m3
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50 100 150 200 250 20 40 60 80 ERIC on hyperwashed pulp (ppm) 50 54 58 62 66 70 Brightness on fibre fraction (% ISO)

MC dispersing HC dispersing HC dispersing + P chemicals

Estimated volume energy Cm.Em (kWh/m3)

Empty symbol brightness Full symbol ERIC

Dispersing between two deinking loops Incidence on optical properties

  • The higher the Ev, the better the ink detachment
  • Brightness gain represents +2% ISO
  • P bleaching allows +5% ISO
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100 200 300 400 500 600 20 40 60 80 ERIC on floated pulp (ppm) 50 54 58 62 66 70 Brightness on floated pulp (% ISO)

MC dispersing HC dispersing HC dispersing + P chemicals

Estimated volume energy Cm.Em

Empty symbol brightness Full symbol ERIC

Dispersing between two deinking loops Incidence on optical properties

  • After 1 deinking loop, ERIC ~ 450 ppm
  • Implementation of second deinking loop after thickening

allows to reach 300 ppm

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Dispersing between two deinking loops Incidence on optical properties

  • Characteristic curve whatever the dispersing parameters
  • An increase in Ev is responsible for ink fragmentation and

therefore a reduction in ink removal even if ink detachment

100 200 300 400 500 600 20 40 60 80 ERIC on floated pulp (ppm) 50 54 58 62 66 70 Brightness on floated pulp (% ISO)

MC dispersing HC dispersing HC dispersing + P chemicals

Estimated volume energy Cm.Em

Empty symbol brightness Full symbol ERIC

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100 200 300 400 500 600 20 40 60 80 ERIC on floated pulp (ppm) 50 54 58 62 66 70 Brightness on floated pulp (% ISO)

MC dispersing HC dispersing HC dispersing + P chemicals

Estimated volume energy Cm.Em

Empty symbol brightness Full symbol ERIC

Dispersing between two deinking loops Incidence on optical properties

  • Decrease in ink removal is responsible for a decrease in

brightness of floated pulp

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50 100 150 200 250 300 20 40 60 80 ERIC on fibre or specks contamination 100 200 300 400 500 600 ERIC after flotation on whole pulp Estimated volume energy Cm.Em ( / ) Ink content after flotation

Dispersing between 2 deinking loops Incidence on optical properties

  • Decrease in ink removal efficiency for an increase in Ev

After 1st deinking loop Post flotation (without dispersing)

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50 100 150 200 250 300 20 40 60 80 ERIC on fibre or specks contamination 100 200 300 400 500 600 ERIC after flotation on whole pulp Estimated volume energy Cm.Em ( / ) Ink content after flotation Ink detachment

Dispersing between 2 deinking loops Incidence on optical properties

  • Decrease in ink removal efficiency for an increase in Ev
  • No significant ink detachment improvement if Ev>10 kWh/m3
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50 100 150 200 250 300 20 40 60 80 ERIC on fibre or specks contamination 100 200 300 400 500 600 ERIC after flotation on whole pulp Estimated volume energy Cm.Em Ink content after flotation Ink detachment Specks

Dispersing between 2 deinking loops Incidence on optical properties

  • Decrease in ink removal efficiency for an increase in Ev
  • No significant ink detachment improvement if Ev>10 kWh/m3
  • No significant speck reduction if Ev>20 kWh/m3
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50 100 150 200 250 300 20 40 60 80 ERIC on fibre or specks contamination 100 200 300 400 500 600 ERIC after flotation on whole pulp Estimated volume energy Cm.Em Ink content after flotation Ink detachment Specks

Dispersing between 2 deinking loops Incidence on optical properties

  • Decrease in ink removal efficiency for an increase in Ev
  • No significant ink detachment improvement if Ev>10 kWh/m3
  • No significant speck reduction if Ev>20 kWh/m3

Fibre degradation (Ev>20) Cm=20% - 100 kWh/T Cm=30% - 66 kWh/T Cm=20% - 50 kWh/T Cm=30% - 33 kWh/T

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Guideline

  • Introduction
  • Theoretical aspects
  • High-speed dispersing between two deinking loops
  • Raw material and flowsheet
  • Incidence of thickening, steam and peroxide bleaching

chemicals

  • Consequences on morphological fibre characteristics
  • Consequences on optical properties
  • Conclusions
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Conclusions

  • High-speed dispersing between 2 deinking loops:
  • Reduction in speck contamination
  • Ink detachment improvement
  • Degradation of post-flotation efficiency due to ink

fragmentation

  • Fibre degradation (no significant effect for conventional

energy application)

  • Possibility to characterize it through volume energy

approach

  • Whatever the consistency
  • Whatever the specific energy applied
  • Independent from P liquor (ink, specks behaviour)
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66 33 Specific energy (kWh/t) Cm = 30% 100 50 Specific energy (kWh/t) Cm = 20 % Fibre degradation Speck fragmentation Ink detachment Decrease in ink removal 20 10 Estimated volume energy (kWh/m3) 66 33 Specific energy (kWh/t) Cm = 30% 100 50 Specific energy (kWh/t) Cm = 20 % Fibre degradation Speck fragmentation Ink detachment Decrease in ink removal 20 10 Estimated volume energy (kWh/m3) Phenomena

Conclusions Role of estimated volume energy

  • Most significant effect of high-speed disperser

between two deinking loops

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66 33 Specific energy (kWh/t) Cm = 30% 100 50 Specific energy (kWh/t) Cm = 20 % Fibre degradation Speck fragmentation Ink detachment Decrease in ink removal 20 10 Estimated volume energy (kWh/m3) 66 33 Specific energy (kWh/t) Cm = 30% 100 50 Specific energy (kWh/t) Cm = 20 % Fibre degradation Speck fragmentation Ink detachment Decrease in ink removal 20 10 Estimated volume energy (kWh/m3) Phenomena

Conclusions Role of estimated volume energy

  • Practical consequences:
  • Reduction in energy is

required to reduce ink fragmentation and to reduce negative impact on flotation efficiency

  • Ink detachment requires energy application (but plateau for

Ev>10 kWh/m3

50 kWh/T at Cm=20% 33 kWh/T at Cm=30%

  • Reduction in speck contamination requires energy application

(but plateau for Ev>20 kWh/m3

100 kWh/T at Cm=20% 66 kWh/T at Cm=30%

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66 33 Specific energy (kWh/t) Cm = 30% 100 50 Specific energy (kWh/t) Cm = 20 % Fibre degradation Speck fragmentation Ink detachment Decrease in ink removal 20 10 Estimated volume energy (kWh/m3) 66 33 Specific energy (kWh/t) Cm = 30% 100 50 Specific energy (kWh/t) Cm = 20 % Fibre degradation Speck fragmentation Ink detachment Decrease in ink removal 20 10 Estimated volume energy (kWh/m3) Phenomena

Conclusions Role of estimated volume energy

  • Dispersing parameters

should therefore take into account these antagonist phenomena according to the inlet of this stage

  • If cleanliness is acceptable after the 1st deinking loop, not

necessary to put high dispersing energy

  • If cleanliness is poor (raw material composition, summer), the

energy must be adapted to the target of the mill in order to reduce the drawbacks (in any case, Ev<20 kWh/m3)

  • In any case, ERIC and speck measurements at the inlet (or
  • utlet) of the disperser is required to adapt running dispersing

parameters

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High-speed dispersing between 2 deinking loops: are there optimisation possibilities?

CTP and CTPi members, all the companies having supported this project, as well as the technicians having carried out all the experimental part are acknowledged Thank you for your attention