Membrane treatment of alkaline bleaching effluent on a kraft pulp mill

FEDERAL UNIVERSITY OF VIÇOSA DEPARTMENT OF FOREST ENGINEERING LABORATORY OF PULP AND PAPER Membrane treatment of alkaline bleaching effluent on a kraft pulp mill Rafael Quezada, Claudio Mudadu Silva, Leif Nilsson Christian Hoffstedt and Niklas Berling

Outline Introduction Objectives Results Membrane treatment of alkaline bleaching effluent Effects of the (EPO) membrane filtration on the effluent treatment plant Membrane permeate recycling to the bleaching plant Membrane retentate send to black liquor evaporation Conclusions

Effluent generation 1,3 6,0 4 10 15 30 4 7 WOODYARD COOKING BLEACHING DRYNG MACHINE EVAPORATORS 0,5 2,0 Water consumption Bleaching area: 45.000 m 3 /d Total: 65.000 m 3 /d RECOVERY BOILER CAUSTICIZING 1,0 2,0 2,0 4,0 Volume (m 3 /adt)

Membrane treatment Module (EPO) filtrate Membrane Retentate Permeate

Bleaching sequence NaOH D (EPO) D D Pre O2 Pulp D (EPO) D D ClO 2 Acid effluent (EPO) filtrate Alkaline effluent

Objectives Evaluate the membrane treatment of (EPO) filtrates from a kraft pulp mill Specific objectives a) Compare three configurations of membrane to treat alkaline (EPO) filtrate of a kraft pulp mill using pilot plants and determine the best operation conditions; b) Study the effect of the (EPO) filtrate membrane treatment on the effluent treatment plant; c) Evaluate the feasibility of recycling of the UF permeate within the bleaching plant; d) Evaluate the feasibility to send the UF retentate to the black liquor evaporation sector

Membrane treatment of alkaline bleaching effluent

Membrane treatment Experimental set-up Membrane configuration selection (UF, UF + NF, NF) Optimal condition determination Long-term operation

Membrane treatment Pilot plants

Membrane treatment The nanofiltration membranes require a pretreatment to reduce temperature and neutralize ph; In order to select the best option it was considered not only the selectivity but also the costs and operation simplicity; The selected configuration was ultrafiltration; The best condition for higher permeate flux (over 200 L/m 2 h) was 3,0 m/s of cross-flow velocity and 7 bar of TMP, for a COD removal and color of 58% and 91%, respectively.

Effects of the (EPO) UF on the effluent treatment plant

Effects on the ETP Scenario 1 NaOH Pre O2 Pulp D (EPO) D D ClO 2 Permeate Acid effluent Retentate ETP

Effects on the ETP Scenario 2 NaOH Pre O2 Pulp D (EPO) D D ClO 2 Permeate Acid effluent Chemical recovery process Retentate ETP

Effects on the ETP Lab. simulation Biological treatment Tertiary treatment Reference Scenario 1 Effluent with (EPO) UF permeate Scenario 2 Effluent without (EPO) filtrate. UF permeate is recycled

Effects on the ETP Effects of the UF on the Effluent Treatment Plant Parameter Scenario 1 Scenario 2 Softwood Hardwood Softwood Hardwood COD reduction efficiency +10,1% + 9,8 % + 6,0 % + 8,1 % Final color - 9,8 % - 8,0 % -8,3 % - 8,0 % Biological sludge production 0 % 0 % - 20,3 % - 17,1 % Energy consumption 0 % 0 % - 20,3 % -17,1 % Coagulant dosage - 30 % - 37 % - 40 % - 40 % Tertiary sludge production - 28 % - 35 % - 44 % - 46 % (+) Increase; (-) decrease

Membrane permeate recycling to the bleaching plant

Permeate recycling Software simulation (WinGEMS); Steady state model approach; Hot water on the EOP-press is stepwise replaced with permeate from the membrane filtration unit all washing liquor on the press is permeate; Same efficiency assumed at different filtrate concentrations although a different filtrate composition can be expected when recycling the permeate on the EOP-press. EPO permeate available (m 3 /adt) Hot water used on EPOpress (m 3 /adt) Softwood 8,4 5,8 Hardwood 6,2 5,4

CaCO 3 g/adt CaCO 3 g/adt Permeate recycling CaCO 3 formation 200 150 100 (EPO) Stage (EPO) Filtrate Supersaturation limit Softwood campaign 50 0 0 20 40 60 80 100 Hot water on EOP-press replaced with permeate (%) 300 250 200 150 100 50 (EPO) Stage (EPO) Filtrate Supersaturation limit Hardwood campaign 0 0 20 40 60 80 100 Hot water on EOP-press replaced with permeate (%)

Mg(OH) 2 g/adt Mg(OH) 2 g/adt Permeate recycling Mg(OH) 2 formation 250 200 150 100 50 (EPO) Stage (EPO) Filtrate Softwood campaign 0 80 0 20 40 60 80 100 Hot water on EOP-press replaced with permeate (%) 60 40 20 0 (EPO) Stage (EPO) Filtrate 0 20 40 60 80 100 Hot water on EOP-press replaced with permeate (%) Hardwood campaign

UF retentate send to black liquor evaporation

Retentate reuse Hardwood Softwood Parameter Weak black Retentate CI Weak black Retentate liquor (kg/h) (kg/h) (%) liquor (kg/h) (kg/h) CI (%) Na 26380 10,28 0,04 35596 11,74 0,03 Ca 65 0,43 0,66 33 0,37 1,13 K 361 0,28 0,08 3379 0,29 0,01 Mg 25,5 0,34 1,33 36,6 0,95 2,59 Mn 8,0 0,16 1,96 4,0 0,05 1,24 Ba 1,59 0,003 0,18 0,22 0,001 0,39 Al 12,7 0,22 1,72 8,8 0,23 2,63 Si 76,3 0,11 0,14 40,2 0,34 0,84 P 55,0 0,06 0,10 16,1 0,06 0,34 Cl 239 0,83 0,35 576 1,25 0,22 SO 4 7415 3,55 0,05 4147 1,79 0,04 CI= Concentration increment of the element on the weak black liquor after adding the (EPO) retentate

Conclusions The treatment of the (EPO) filtrate by tight UF allows an increase on the COD removal efficiency by 10% in the biological treatment plant. It also decreased the color on the treated effluent by approximately 9%; The recycle of the resulting UF permeate in the bleaching area is the best option available for the reuse of this current; It can increase the efficiency of COD reduction in 8%, and 20% reduction in the generation of biological sludge, 45% of tertiary sludge and 40% less coagulant. Water economy: 200 L/s (17.280 m 3 /d)

Conclusions In the hardwood and in the softwood case, 100% replacement of hot water on EPO-press is possible (5,4 m 3 /adt and 5,8 m 3 /adt) Small CaCO 3 (s)-formation in EOP-filtrate above 50% replacement of hot water due to high carbonate content according to equilibrium calculations Supersaturation calculations indicate that the precipitations will not start to form when replacing 100% of the hot water with permeate It is expected that the relation of S/Na 2 remain unchanged after the addition of the retentate to the black liquor stream, therefore the recovery boiler chemical performance will not be affected

Membrane configuration selectivity PCI modules Cost information Industrial design Membrane performance experiment Characterization of filtrates, permeate and retentate

MICRO FILTRATION ULTRA FILTRATION NANO FILTRATON REVERSE OSMOSE Diâmetro Poros 0,1-10 m 0,02-0,1 m 500-20.000 Da <500 Da Pressão 70-350 KPa 170-850 KPa 500-1500 KPa 3500-5000 KPa Suspended Solids Bacteria Virus Multivalent ions Monovalent Ions Water Mudado, 2008

PCI B1 Module lenght (m) 1,22 2,44 3,66 Area (m 2 ) 0,88 1,75 2,63

Membrane Temperature Press PCI ESP04 70 75 C Above 8 bar ph 11 11,5 Permeate recuperation 98 99% Permeate flux Area 90 l/m2.h 7.971,6 m2 Lines 3 Steps/Line 7 Modules/steps 146 Investment: $15.000.000 USD Energy: $1.200.000 USD/year (1.485 kw) Membrane: $920.000 USD/year Cleaning: $250.000 USD/year

P1 P2 P3 P4 P5 P6 Permeate 7 R1 R2 R3 R4 R5 R6 Retentate 7 (EPO) filtrate

Permeate flux, L/m 2.h Volumetric concentration factor (VCF)

Raw material Eucalyptus Pine Parameter Na Ca K Mg Mn Ba Al Si P Cl SO 4 Units mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l Permeate (198 L/s) 666 0,95 12,7 0,09 0,01 0,2 4,8 163,7 Retentate (2 L/s) 1428 59,9 39,18 47 21,71 0,391 30,5 14,9 7,69 115 492,8 D0 filtrate 575 26 33 3,1 1 0,05 0,37 - - - - (EPO) filtrate 625 2,6 7,3 0,6 0,15 0,02 0,26 - - - - D1 filtrate ND ND ND ND ND ND 0,004 - - - - D2 filtrate 381 5,25 4,5 1,1 0,08 0,04 0,31 - - - - Water 150 1,2 1,6 0,3 0,01 0,01 0,31 - - - - Permeate (198 L/s) 694,5 1,36 9,34 0,07 0,005 0,14 8,1 142,7 Retentate (2 L/s) 1630 51,4 40,56 131,8 6,94 0,119 32 46,6 7,6 173 248,3 D0 filtrate 95,2 31,9 31,1 10,5 0,51 0,33 0,45 7,2 - - 790 (EPO) filtrate 603 8,51 11,8 2,2 0,1 0,07 0,2 8,2 - - 250 D1 filtrate 89,7 32,5 34,6 15,9 0,45 0,36 0,69 25,3 - - 370 D2 filtrate 105 15,1 5,1 4 0,09 0,06 0,21 9,3 - - 230 Water 162 3,22 0,6 0,5 0,03 0,01 0,22 4,3 - - -