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 deinking loops • Raw material and flowsheet • Consequences on morphological fibre characteristics • Consequences on optical properties • Conclusions Niagara Falls / BF / Sept. 2007 2
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 Niagara Falls / BF / Sept. 2007 3
Introduction Objectives • To determine the incidence of dispersing parameters on • 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 Niagara Falls / BF / Sept. 2007 4
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 Niagara Falls / BF / Sept. 2007 5
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) Niagara Falls / BF / Sept. 2007 6
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 (L B ) � 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 Niagara Falls / BF / Sept. 2007 7
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 overall and composite information on pulping phenomena (overall approach for LC, HC and drum pulpers) Niagara Falls / BF / Sept. 2007 8
Theoretical aspect Fragmentation approach • Dispersing can be classified as fragmentation No fragmentation if the mechanical force is less intense than the resistive strength of the particles considered Dispersing Fragmentation if the mechanical force is intense enough compared to the resistive strength of the particles considered Niagara Falls / BF / Sept. 2007 9
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 Niagara Falls / BF / Sept. 2007 10
Theoretical aspects Application of Volume Energy (Ev) 2500 Low Consistency High-speed Dispersing ERIC on entire pulp (ppm) 2000 Medium Consistency 1500 High Consistency 1000 Low-speed Medium Kneading Consistency 500 High Specific energy consumption (kWh/T) Consistency 0 0 50 100 150 200 • No overall approach of ink fragmentation by considering specific energy consumption Niagara Falls / BF / Sept. 2007 11
Theoretical aspects Application of Volume Energy (Ev) 2500 Low Consistency High-speed Dispersing ERIC on entire pulp (ppm) 2000 Medium Consistency 1500 High Consistency 1000 Low-speed Medium Kneading Consistency 500 High Estimated volume energy (Cm.Em) Consistency 0 0 20 40 60 80 100 • Possible to obtain a characteristic curve by considering volume energy whatever the dispersing unit Niagara Falls / BF / Sept. 2007 12
Theoretical aspects Application of Volume Energy (Ev) 3000 ERIC entire pulp = 2100 - 750.e -0.0642.Cm.Em Ink fragmentation modelling through r² = 0.88 2500 volume energy approach Calculated data 2000 ERIC entire pulp in ppm 1500 Cm : mass consistency 1000 expressed as fraction (-) 500 Em : specific energy Experimental data consumption (kWh/T) 0 0 1000 2000 3000 • 1st order kinetic can describe ink fragmentation ERIC entire pulp = 2100 – 750.e -0.0642 Cm.Em Niagara Falls / BF / Sept. 2007 13
Theoretical aspects Application of Volume Energy (Ev) Low ERIC on hyperwashed pulp (ppm) 400 Consistency High-speed Dispersing Medium Consistency 300 High Consistency 200 Ink detachment 100 and ink redeposition Estimated volume energy Cm.Em (kWh/m3) 0 0 20 40 60 80 100 • Ink detachment/redeposition can be described by estimated volume energy Niagara Falls / BF / Sept. 2007 14
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 Niagara Falls / BF / Sept. 2007 15
Methodology Miles and May (1990, 1991) Ec can be viewed as an • Refining (and dispersing) can be characterized by approximation of volume • The number of impact imparted to a fibre (n) energy • The specific energy per bar impact imposed during refining Other parameters are (e) constant in the present study • E = n . e E: specific energy consumption in J/kg c : pulp mass concentration ⎛ ⎞ r 2 : outer radius dispersing zone r ⎜ ⎟ N h a E c µ = ⋅ ⋅ r 2 n r 1 : inner radius dispersing zone ln ⎜ ⎟ − 2 µ 2 w r r r ⎝ ⎠ ( ) w : rotational speed t 2 1 1 µ r : radial coefficient of friction − 2 2 w r r ( ) µ µ t : tangential coefficient of friction 2 1 = ⋅ ⋅ t e ⎛ ⎞ N : Average number of bar per unit length of arc µ r ⎜ ⎟ r 2 N h a c ln h : number of rotating disk ⎜ ⎟ r ⎝ ⎠ 1 a : constant of friction Niagara Falls / BF / Sept. 2007 16
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 Niagara Falls / BF / Sept. 2007 17
Raw material and process parameters • 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 • 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 Niagara Falls / BF / Sept. 2007 18
Raw material and process parameters steam MC thickening in vacuum filter Fine screening Kadant Lamort CH3 // 20/100 steam HC thickening in screw press Steam + chemical 1% NaOH 2.5% Silicate Pilot flotation 1% Peroxide For each dispersing treatment, several Niagara Falls / BF / Sept. 2007 19 specific energies are applied
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 Niagara Falls / BF / Sept. 2007 20
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