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 TOTAL YIELD LOSSES % of Feed Solids 20.0 18.0 16.0 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 Specific Air Volume, l/kg 800 700 600 500 400 300 200 100 0 Experimental Conditions 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 Inks Stickies Fibers Plastics Inorganic Ash Fillers Minerals in wood fiber
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 1.5 1.3 1.1 0.9 0.7 250 200 150 100 50 0 0.5 % Increase in Specific Air Volume Cell Operating Consistency
Higher SAV increases % yield losses Mill Operating Data 600 14 Free Ink, ppm 500 400 300 200 100 FREE INK YIELD LOSSES 12 10 8 6 4 2 Yield Loss, % of feed solids 0 0 50 100 150 200 0 Specific Air Volume, l/kg
46 45 44 43 42 41 40 39 38 37 36 Air holdup and bubble size is dynamic in an operating flotation cell Changes in Indicated Level with Air Holdup 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 1 0.9 0.8 0.7 0.6 0.5 Indicated Level, % Measured Consistency Cell level Consistency
Results of Laboratory Study
Previous Benchmarking study showed that Filler Losses are unique to each System 80.0 70.0 FILLER LOSSES, % of feed filler content 60.0 50.0 40.0 30.0 20.0 10.0 0.0 MILL A MILL B MILL C MILL D 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, % of Cell Feed Ash 60 50 40 30 20 10 0 Filler Losses at Different Operating Consistencies 0 200 400 600 800 SAV, l/kg 0.50% 1% 1.50%
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 1000 SVA vs Cell Consistency 900 SAV, l/kg 800 700 600 500 Free Ink=100 Free Ink=150 Free Ink=200 400 300 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 Free Ink in Cell Accepts, ERIC 400 350 300 250 200 150 Ink Removal vs. Cell Consistency 0.5 0.7 0.9 1.1 1.3 1.5 Cell Feed Consistency SAV=200 l/kg SAV=300 l/kg SAV=400 l/kg
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 58 57 56 55 54 53 52 51 50 Brightness/Yield Loss at Different Operating Consistencies 0 2 4 6 8 10 % Combustible Solids Loss 0.50% 1% 1.50%
At higher operating consistencies, yield losses necessary to achieve a given ink removal are reduced Combustible Losses, % of Cell Feed 10 8 6 4 2 0 Yield Losses at Different Operating Consistencies 0 100 200 300 400 500 Free Ink in Cell Accepts, ERIC 0.50% 1% 1.50%
Free Ink in Cell Accepts, ERIC 500 450 400 350 300 250 200 150 100 50 0 Yield Losses in Relation to SAV and Ink Removal SAV = 150 l/kg SAV = 425 l/kg SAV = 700 l/kg 0 2 4 6 8 10 Combustible Losses, % of cell feed Cell Feed Consistency 0.5% 1.0% 1.5%
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