Interaction of Flotation Cell Operating Variables

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1 Interaction of Flotation Cell Operating Variables Henry Peters and Tom Remigio Tim Evans and Marc Dagenais

2 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

3 ACI Deinking Plant Total Yield Loss Comparison TOTAL YIELD LOSSES % of Feed Solids FREE INK, ERIC

4 Test Methods Experimental design at varying consistencies and specific air volumes Specific Air Volume, l/kg Experimental Conditions Flotation Cell Consistency, %

5 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

6 ASH test for yield analysis Sample ashed At 525C Combustible materials Inks Stickies Fibers Plastics Inorganic Ash Fillers Minerals in wood fiber

7 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.

8 Specific air volume increases as cell consistency is lowered Specific Air Volume vs. Consistency % Increase in Specific Air Volume Cell Operating Consistency

9 Higher SAV increases % yield losses Mill Operating Data Free Ink, ppm FREE INK YIELD LOSSES Yield Loss, % of feed solids Specific Air Volume, l/kg

10 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 Indicated Level, % Measured Consistency Cell level Consistency

11 Results of Laboratory Study

12 Previous Benchmarking study showed that Filler Losses are unique to each System FILLER LOSSES, % of feed filler content MILL A MILL B MILL C MILL D COMBUSTIBLE LOSSES, % of cell feed

13 Laboratory study showed that filler losses are independent of cell operating consistency Filler Losses, % of Cell Feed Ash Filler Losses at Different Operating Consistencies SAV, l/kg 0.50% 1% 1.50%

14 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

15 Lowest SAV to achieve a target ink removal efficiency is at 0.8% consistency 1000 SVA vs Cell Consistency 900 SAV, l/kg Free Ink=100 Free Ink=150 Free Ink= Cell Feed Consistency, %

16 For cells with fixed air input, best ink removal can be achieved at about 0.8% operating consistency Free Ink in Cell Accepts, ERIC Ink Removal vs. Cell Consistency Cell Feed Consistency SAV=200 l/kg SAV=300 l/kg SAV=400 l/kg

17 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

18 Ink is a major component of combustible losses as losses increase, pulp brightness improves Brightness Brightness/Yield Loss at Different Operating Consistencies % Combustible Solids Loss 0.50% 1% 1.50%

19 At higher operating consistencies, yield losses necessary to achieve a given ink removal are reduced Combustible Losses, % of Cell Feed Yield Losses at Different Operating Consistencies Free Ink in Cell Accepts, ERIC 0.50% 1% 1.50%

20 Free Ink in Cell Accepts, ERIC Yield Losses in Relation to SAV and Ink Removal SAV = 150 l/kg SAV = 425 l/kg SAV = 700 l/kg Combustible Losses, % of cell feed Cell Feed Consistency 0.5% 1.0% 1.5%

21 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