Brown Stock Washing Optimization and Research

Studies Field Results

Riku Kopra, Mikkeli University of Applied SciencesRiku.kopra@mamk.fi

Content

1. Personal history2. Publications3. Results of brown stock washing

studies4. Conclusion5. Example of the waste water case

Personal history- Engineer of Paper technology, Tampere

University of Applied sciences, 2000 • Practical training -97, Metsä-Rauma- Master of Science in Industrial Environmental

Technology, University of Oulu 2004• Master thesis: Study of pulp washing in five different kraft

pulp mill- Researcher LUT, Savonlinna, 9/2004 – 10/2005- Researcher MAMK, Savonlinna 11/2005 →- Postgraduate, Aalto University 2006 →• Academic dissertation: Kraft pulp wash loss and its reliable

measurement at pulp mill, 2012

Publications

1) Refractive index measurements for brown stock washing loss - laboratory investigations, APPITA JOURNAL vol 61(5), 2008.

• Usability of Refactometer to Measure Washing Loss in Chemical Pulping

2) Refractive index measurements for brown stock washing loss - mill investigations, APPITA JOURNAL vol 63(2), 2010 and 63rd APPITA CONFERENCE

• Usability of Refactometer to Measure Washing Loss in Chemical Pulping• Different measurement methods in determining brown stock washing loss

were compared, Washing efficiency E10 was calculated, refractometer measurement in the oxygen delignification feed

3) Optimization of pressure filter performance by refractometer - Mill investigations, APPITA JOURNAL vol 64(1) and 64th APPITA CONFERENCE

• Optimization of different variables which affect to pressure filters performance, Refractometer measurement in the all filtrate fractions of single washer

Publications4) Improving brown stock washing by using on-line measurement –

mill investigations, ABTCP-TAPPI 2010 CONFERENCE and O’PAPEL (under review)

• Optimisation of brown stock washing, digester washing, pressure diffuser washing, double filter washing, the effect of the washing to oxygen delignification

5) Optimization of wash water usage in brown stock washing, TAPPI PEERS 2010 CONFERENCE

• Utilization of Real-time Refractometer Measuring Results in Chemical Pulping

6) Refractometer and its ability to measure dissolved dry solids at low concentrations, 65th APPITA CONFERENCE

• Investigation of Real-time Refractometer Measurement Applied in an Activated Sludge Plant

Master thesis• Helttunen Jukka: Washing loss on-line measurement in kraft pulping• Karjalainen Simo: The optimization of the DD-washer• Kari Erkki: Improving the efficiency of brown stock washing by utilizing

real-time measurements

Content of mill studies1) Target2) Arrangement of mill tests3) Comparison of different measurement

methods4) The effect of pulp consistency to washers

operation5) The effect of wash liquor amount to washers

operation6) The effect of the brown stock washing to

performance of oxygen delignification and to economy of pulp mill

7) Washer operation8) Conclusions

Brownstock washing• Digester• Post-digester• Post O2-stage• Post screening

Target

Pulp washing in bleaching

• Series of investigations to find solutions that minimize washing loss and consume less energy, water and chemicals

Arrangement 1

Arrangement 2

Arrangement 3

Results

• Comparison of different measurement methods

Normalized wash losses

• All devices detect wash loss • Proportional variances are constant

0102030405060708090

100

Diffuser filtrate(output )

RR-washer 1-washing filtrate

RR-washer 2-washing filtrate

O2-stage pulp(input)

COD Dry solids, SFS3008Dry solids by refractometer Conductivity

SF-3008 vs. Refractometer in filtrates

• Correctly calibrated refractometer measures exactly DDS. • The wood species had resonance for the measuring result

y = 0,8403xR2 = 0,9773

y = 0,9381xR2 = 0,9708

0,01,02,03,04,05,06,07,08,09,0

0,0 2,0 4,0 6,0 8,0 10,0 Dry Solids (SFS3008), % by weight

Dry

sol

ids

(ref

ract

omet

er),

%

by

wei

ght

Hardw ood Softw ood

Refractometer vs. COD in filtrates

• The correlation between COD and dissolved dry solid content measured by the refractometer

y = 14,896x - 22,074R2 = 0,9947

y = 12,459x - 11,999R2 = 0,9984

0

20

40

60

80

100

120

0 2 4 6 8 10Dry solids (refractometer), % by weight

CO

D, g

/l

Hardwood Softwood

Conductivity vs. refractometer in filtrates

• The correlation is not linear • Conductivity increase begins to slow down

with a rise in dry solids concentration

20

25

30

35

40

45

50

0 2 4 6 8 10Dry solids (refractometer), % by weight

Cond

uctiv

ity, m

S/cm

Hardwood Softwood

Low %b.w. Higher %b.w.

Conductivity vs. Liquid concentrationSource: Pihkala, J.

Filtered results of Refractometer and COD-analysis

• Refractometer measurement follows the mills COD-laboratory analysis considering level differences

050

100150200250300350400

10.1.

2007

12.1.

2007

16.1.

2007

23.1.

2007

9.2.20

07

14.2.

2007

22.2.

2007

27.2.

2007

6.3.20

07

8.3.20

07

29.3.

2007

Con

cent

ratio

n, k

g di

ssol

ved

dry

solid

s/A

dt

050100150200250300350400

kg C

OD

/Adt

kg COD/ADt kg dry solids/ADt

Results

• The effect of pulp consistency to washers operation

Effect of washing consistency on washing results

• A sufficiently high consistency of feed pulp to the washer enabled high washing consistency → is an essential requirement for effective and economical washing of pulp

Pressure Diffuser’s Feed Consistency Effect

• With a higher feed consistency, the washing efficiency is increased

Effect of Feed Consistency on Discharge Consistency (Hardwood)

• Too high feed consistency harmfully affects the double filter’s washing performance

• In the literature: “When the washer operates at design capacity the optimum feed consistency is between 1.0 and 1.25% for softwood and 1.1 and 1.5% for hardwood”

10,511,011,512,012,513,013,514,014,515,015,5

1,1 1,3 1,5 1,7 1,9 2,1

Feed consistency, [%]

Dis

char

ge

con

sist

ency

, [%

]

Optimum range Poor wash results

Results

• The effect of wash liquor amount to washers operation

Effect of dilution factor on washing results

• Dilution factor should be above 1 to guarantee unobstructed washer performance

• The real-time results are similar to literatureOptimum range

1-3Normal practice

up to 5

Effect of Dilution Ratio on E10 and on Washing Loss

• The dilution ratio notably affects the pressure diffuser’s washing result

[ ][ ]slinliquorwash

sloutfiltratewashratioDilution/),(

/),(=

0

1

2

3

4

5

6

7

0,90 0,92 0,94 0,96 0,98 1,00 1,02

Dilution ratio

E 10

1300

1350

1400

1450

1500

1550

0,90 0,92 0,94 0,96 0,98 1,00 1,02

Dilution ratio

Was

hing

loss

, [kg

DS/

BD

t]

Utilising radial displacement washing in the digester

• Bypass was decreased and the amount of wash liquor fed into the digester was increased (into the central distribution chamber). The same amount of filtrate from the wash circulation was extracted.

• The digester’s washing result can be increased by utilising radial displacement washing.

Results

• The effect of the brown stock washing on the performance of oxygen delignification and on the economy of pulp mill

Effects of Washing Loss on Oxygen Delignification (Hardwood)

• When the amount of the washing loss increases more alkali is consumed in oxygen delignification

• The reason for this is that e.g. alkali is consumed in the neutralization reactions of the acids originated from the cooking

0,000,250,500,751,001,251,501,752,002,252,50

100 200 300 400 500

Washing loss to oxygen delignification, [kgDS/BDt]

Alka

li ch

arge

to O

2-st

age

[kgN

aOH/

BDt]

/ Kap

pare

duct

ion

in O

2-st

age

[%]

The Effect of Washing Loss on Oxygen Reactor’s Temperature (Softwood)

• The temperature in the oxygen reactor correlates with the amount of washing loss

88,0

89,0

90,0

91,0

92,0

93,0

94,0

95,0

96,0

100 200 300 400 500

Washing loss to oxygen delignification, (kgDS/BDt)

Tem

pera

ture

in o

xyge

n

reac

tor,

(ºC)

The Effect of Dilution Factor on Evaporation Energy Costs

• At this mill experiment increasing the dilution factor by 1 unit, evaporation costs increase on an average by 1.5 €/BDt.

10

11

12

13

14

15

16

17

0 0,5 1 1,5 2 2,5 3 3,5

Dilution factor, smooth 4h, (t/BDt)

Evap

orat

ion

ener

gy c

ost,

(€/B

Dt)

The Effect of Dilution Factor onNaOH Make-Up Costs

• At this mill experiment increasing the dilution factor by 1 unit, the make-up chemical cost as NaOH decreases on an average by 1.0 €/BDt.

-10123456789

-1 0 1 2 3 4 5Dilution factor, smooth 4h, (t/BDt)

NaO

H co

st fo

r mak

e-up

, sm

ooth

4h

, (€/

BDt)

Results

• Washer operation

Effect of the Downward Velocity of the Pressure Diffuser Screen

• The downward velocity of the screen notably affects the pressure diffuser’s washing result

• In literature: “The optimum velocity ratio should be slightly higher than one being from 1.1 to 1.3.”

Optimum range Optimum range Poor wash results

Effect of seal bars distance on washing results

• The distance of the seal bar from the drum has fundamental effect on the DR-value

• An unbalanced seal bar caused wash liquid to escape from the 1st stage to the 2nd stage

Conclusions•By controlling the performance of washers (cleanness of the screens, velocity of the screens, seal bars distance, rotation speed of drum etc.) and by changing process conditions (temperature, pH, consistency, wash water amount) it is possible to improve the effectiveness of washing line.

→ Continuous measurements are needed for monitoring

•By using refractometer measurements, TDS changes in the incoming washer flows (liquid and pulp suspension) can be detected immediately and reliably

Conclusions

• By using refractometers and data-analyses tools, it is possible to discover the black spots of the washing line and to evaluate the washing result continuously

• This allows for improved washing efficiency and reduced water consumption, which had clear effect on economy of other sub process like evaporation, bleaching and waste water treatment.

• Refractometers provide whole new possibilites for implementing higher level process optimization, e.g. at the whole washing department

Example of the waste water case

• Investigation of Real-time Refractometer Measurement Applied in an Activated Sludge Plant

Target• Identify concentration level changes, as well as

compositional changes in wastewater.• Find a new way to measure wastewater

parameters’ limit values.

Refractometer Installation Points in an Activated Sludge Plant (Mill Tests)

0,24

0,26

0,28

0,3

0,32

0,34

0 500 1000 1500Dis

solv

ed d

ry s

olid

s,

%

by

wei

ght

Outgoing wastewater

Waste water,Lignin, NaOH, Na2SO4, NaCl, Formic acid, Phosphoric acid

The Effects of Adding Six Different Chemicals on TDSref and Conductivity

2,50

2,65

2,80

2,95

3,10

3,25

3,40

0 1000 2000 3000 4000 5000

Con

duct

ivity

, mS/

cm

Outgoing wastewater

Waste water, Lignin, NaOH, Na2SO4, NaCl, Formic acid, Phosphoric acid

6

7

8

9

10

0 10 20 30 40 50 60

pH

Amount of chemicals used, g

Outgoing wastewater

Waste water,Lignin, NaOH, Na2SO4, NaCl, Formic acid, Phosphoric acid

Added chemicals in adding order:

Wastewater, Lignin, NaOH, NaSO4, NaCl, Formic Acid and Phosphoric Acid.

• Refractometer detects organic and inorganic compounds, while conductivity meter detects only inorganics

On-line TDSref and Conductivity Monitoring of Effluents in an Activated Sludge Plant

• Both measurements indicate changes well in the incoming wastewater but conductivity only shows level changes in the outgoing streams.

• Dissolved dry solids decreases and conductivity remains the same → Changes occur mainly in the organic load.

On-line Monitoring of Effluents with TDSref, Laboratory Analyses of TDSlab and COD

• COD load from organic substances decreases dramatically in wastewater treatment plant, while dissolved solids decrease along with the organic compounds.

Conclusions

• Refractometer measures low, dissolved, dry solids in wastewater treatment accurately.

• Different compounds cause different changes, e.g. pH changes cause sedimentation / dissolving. These phenomena should be better understood.

• In the wastewater treatment organic substances are removed efficiently, COD decreases. Inorganic substances are not removed so efficiently, conductivity does not decrease remarkably → amount of TDS approximately becomes halved

• For on-line control of wastewater treatment efficiency we need simultaneous measurements, refractometer, conductivity and pH.

Thanks

Thank you for your attention!Questions?