Interaction of Flotation Cell Operating Variables Henry Peters and Tom Remigio Tim Evans and Marc Dagenais
Purpose of Study • Previous Abitibi-Consolidated deinking plant benchmarking had shown large variation in ink removal performance between mills • Chemistry and cell design had been identified as the major variables affecting ink removal efficiency and yield losses • Flotation cells were being operated over a range of conditions where consistency and air input were used as a means to control performance, but the relationship between these variables was not well understood • This laboratory study was initiated to better define the effects of changes to the operating handles available to operators
ACI Deinking Plant Total Yield Loss Comparison 20.0 18.0 TOTAL YIELD LOSSES 16.0 % of Feed Solids 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 50 75 100 125 150 175 200 225 250 FREE INK, ERIC
Test Methods • Experimental design at varying consistencies and specific air volumes Experimental Conditions 800 Specific Air Volume, l/kg 700 600 500 400 300 200 100 0 0 0.5 1 1.5 2 Flotation Cell Consistency, %
Test Methods • Pulping in Hobart mixer at 45C, 20% consistency and at 8 kWhr/T SE, standard alkaline chemistry • Flotation in Voith E-18 lab cell with soap, and hardness at 180 ppm, controlled air input • Measurement of yield losses, both combustible and inorganic • Measurement of ink removal performance
ASH test for yield analysis Sample ashed At 525C •Combustible materials •Inorganic Ash •Inks •Fillers •Stickies •Minerals in wood fiber •Fibers •Plastics
Specific Air Volume (SAV) • Litres of air applied over cell line per kg solids in cell feed • Changes with operating consistency • Some cells allow control of air input • As a generality, as more air is applied, bubble surface area available for removal of ink increases • Determines relative potential rejects rate of the cell line. Increased SAV increases yield losses as a % of feed solids.
Specific air volume increases as cell consistency is lowered Specific Air Volume vs. Consistency 250 % Increase in Specific Air Volume 200 150 100 50 0 1.5 1.3 1.1 0.9 0.7 0.5 Cell Operating Consistency
Higher SAV increases % yield losses Mill Operating Data 600 14 Yield Loss, % of feed solids 12 FREE INK 500 YIELD LOSSES Free Ink, ppm 10 400 8 300 6 200 4 100 2 0 0 0 50 100 150 200 Specific Air Volume, l/kg
Air holdup and bubble size is dynamic in an operating flotation cell Changes in Indicated Level with Air Holdup 46 1 45 Measured Consistency 44 0.9 Indicated Level, % 43 42 0.8 41 40 0.7 39 Cell level 38 0.6 Consistency 37 36 0.5 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12 20:24 21:36 22:48 0:00 1:12 2:24 3:36 4:48 6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12 20:24 21:36 22:48 0:00 Time
Results of Laboratory Study
Previous Benchmarking study showed that Filler Losses are unique to each System 80.0 70.0 % of feed filler content FILLER LOSSES, 60.0 50.0 40.0 30.0 MILL A 20.0 MILL B MILL C 10.0 MILL D 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 COMBUSTIBLE LOSSES, % of cell feed
Laboratory study showed that filler losses are independent of cell operating consistency Filler Losses at Different Operating Consistencies 60 % of Cell Feed Ash Filler Losses, 50 40 30 0.50% 1% 20 1.50% 10 0 0 200 400 600 800 SAV, l/kg
Ink removal efficiency and Yield Losses • Operators are always trying to optimize operating costs by improving ink removal and reducing yield losses, which seem to be opposing goals – Choice of system chemistry – Waste paper grades with lower ash levels – Pulper specific energy – Cell operating consistency – Specific air volume – Rejects rate control – Disperging conditions
Lowest SAV to achieve a target ink removal efficiency is at 0.8% consistency SVA vs Cell Consistency 1000 900 800 Free Ink=100 SAV, l/kg Free Ink=150 700 Free Ink=200 600 500 400 300 0.4 0.6 0.8 1 1.2 1.4 1.6 Cell Feed Consistency, %
For cells with fixed air input, best ink removal can be achieved at about 0.8% operating consistency Ink Removal vs. Cell Consistency 400 Free Ink in Cell Accepts, 350 SAV=200 l/kg SAV=300 l/kg 300 ERIC SAV=400 l/kg 250 200 150 0.5 0.7 0.9 1.1 1.3 1.5 Cell Feed Consistency
Yield Losses • Increased rejects rates are typically viewed as necessary for increased ink removal • Work showed that at higher operating consistencies, equivalent ink removal can be achieved with reduced losses
Ink is a major component of combustible losses – as losses increase, pulp brightness improves Brightness/Yield Loss at Different Operating Consistencies 58 57 56 Brightness 55 0.50% 54 1% 53 1.50% 52 51 50 0 2 4 6 8 10 % Combustible Solids Loss
At higher operating consistencies, yield losses necessary to achieve a given ink removal are reduced Yield Losses at Different Operating Consistencies 10 Combustible Losses, 8 % of Cell Feed 6 0.50% 1% 4 1.50% 2 0 0 100 200 300 400 500 Free Ink in Cell Accepts, ERIC
Yield Losses in Relation to SAV and Ink Removal 500 Free Ink in Cell Accepts, ERIC 450 400 SAV = 150 l/kg 350 300 Cell Feed 250 Consistency SAV = 425 l/kg 200 0.5% 1.0% 150 SAV = 700 l/kg 1.5% 100 50 0 0 2 4 6 8 10 Combustible Losses, % of cell feed
Conclusions • There is a relationship between ink removal, specific air volume, consistency, and yield losses • Filler losses are independent of cell operating consistency • Combustible (fiber) losses can be reduced at higher operating consistencies, with higher specific air volumes
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