Brownstock Washing Mill Experiences Chemical and Energy Savings by - - PowerPoint PPT Presentation

Chemical and Energy Savings by Efficient Brownstock Washing – Mill Experiences

Chemical and Energy Savings by Efficient Brownstock Washing – Mill Experiences

Carlos Alberto dos Santos, Mathiesen Group, csantos@grupomathiesen.com Hannu Hämäläinen: Nopco Paper Technology, Finland, hannu.hamalainen@nopco.fi Ariel Lamonato, Mathiesen do Brazil, alamonato@grupomathiesen.com Ramon S. Dorronsoro: Nopco Paper Technology, Spain, ramon.sdorronsoro@nopco.es 7th International Colloquium on Eucalyptus Pulp May 26-29, 2015. Vitória, Espirito Santo, Brazil.

CONTENTS

• Introduction

– Brownstock washing chemistry principles – Defoamer chemistry aspects – How chemistry can improve washing efficiency

• Experimental
• Background mill results
• Results and discussion
• Conclusions
• References

Importance of brownstock washing (BSW)

• It’s a separation process of

– Pulp fibre for papermaking – Washed black liquor with chemical & energy value

• It’s a heterogenous process

– Solid fibre, air and liquid media

• It’s a dynamic process

– Countercurrent wash flow

• It’s a crossroad in fibreline operations

– When BSW is well managed, usually mill is running well in other sections too – When BSW is doing bad, it is negatively seen in other pulp mill sections

Pikka et all Kopra et all

BSW key variables

• Wood (fibre) type

– Surfactant chemistry, fibre mat behaviour

• Equipment design (washer setup)

– DD, press, drum filter, CB, diffusers, chemiwasher

• Operational parameters

– Dilutions, consistencies, tank & vat levels, pressures, temperatures, etc. and process control

• Chemistry

– Often neglected – Washing chemistry, surfactant chemistry

• Application know-how

– Engineers task to improve efficiency !

1 2 ° 1 2 ° 1 2 ° Lamellae

Plateu border

Air in system – foam!

• Foam is a dispersion of gas in liquid that makes a complex network of

interconnected films (lamellaes)

• The lamellae are connected by three and radiate 120° outward from the

connection points, known as plateau borders. Foam lamellae 200x

Conditions to create foam

• Mechanical energy:

– Agitation – Pumping – Blowing of air, etc may increase the total surface area

• Surface active substances
• Speed of foam formation vs break

down of the foam To create foam, work (W) is needed to increase the surface area (ΔA), where γ is the surface tension.

 W A  

Forces affecting foam stability

1) Viscosity

Liquid

–

Surfactant

– – – – – – – – – – – – – –

+ + + + + + + + + + + + + + + – + – – – – 1 2 3

Lamellae

Higher viscosity Higher viscosity Lower viscosity



1



1



2

F F

Surfactant Liquid

2) Electrical double layer (EDL) repulsion 3) Marangoni effects

Foam break down

• Gravitation

– Drainage of liquid to the foam base

• Plateu border pressure

– Drainage of liquid from lamellae to plateu border

• Gas bubbles

– Diffusion of gas from small to larger bubbles due to pressure differences

• Defoamer: surface active substances that spread on the foam lamellaes

and break them down

Thinning lamellae Dewetting and hole formation AW – contact angle Filmthinning due to film drainage and streching Particle must have suficient size to bridge lamellea and be hydrophobe Hole Film thinning AW AW

Lamellae break down by a hydrophobic sphere Lamella break down by hydrophobic liquid



*

Streching due to drainage and capilary pressure Collaps Film thinnin g



* Oil lens Droplet  1 µm Film thinnin g



* Bridging by oil droplet Unstable if * > 90° H

• l

e

Foam break down

Lamellae break down by competing surfactant

Thinning gives rupture of lamellae

Value-adding defoamer approach

• Maximise production rate
• Increase BSW efficiency
• Differing dosing philosophy
• Not to minimize dosage
• Silicone emulsion defoamer should be a BSW

booster

• Allows using less wash liquid
• Reduce evaporation cost and bottleneck
• Cleaner pulp
• Safe to use defoamer, not adhering to pulp /

surfaces

• Defoamer formulated to follow filtrate

A successful BSW improvement program starts with:

 Mill targets, demands and needs  Review audit of process bottlenecks, layout and operation  Tailor made planning and execution of a program:

Program proposal

 Product selection based on lab test and previous experiences  Trial proposal with technical details: dosing points and dosage level, instructions of measures to be taken  Technical support and monitoring during trial, as well as readiness to adjust during trial  Post-trial review and evaluation of added value

Value-adding defoamer approach

Usual Lower Cost Other Expenses Chemicals Steam Investment Other Expenses Value added defoamer Savings $$ Chemicals Steam

Value-adding defoamer approach

Washing Efficiency

– Typically measured by COD carryover to next stage – Mills use some correlations, like COD carryover, soda loss , conductivity in filtrate leaving BSW, it depends case by case.

• Lignin, sulphur compounds, carbohydrates, methanol and other materials that

doesn’t relate well with washing performance and subsequent bleachability of pulp. – Individual washing efficiencies can be calculated – Using E10 can be compared with different consistencies (not practical) – Then, operation remain on:

• COD carryover
• Soda Loss carryover
• Conductivity

Ala-Kaila et all

Experimental

• Industrial full-scale mill trials:

– Provided state-of-art silicone defoamer and washing aid chemicals in same product – Provided application service – Each case designed to follow Clean Pulp philosophy:

• Auditing mill process design and ways of operation
• Technical performance
• Process limitations
• Laboratory screening of defoamer / washing aid
• Selection of best product

Objectives

• Process approach needs to take into account equipment design, operating

parameters, chemistry and application know-how. The concept is centered on maximizing productivity through following measures:

– Maximise production rate (through higher drainage ability and stability/robustness) – Increase BSW efficiency – Reduce bleaching chemical cost and total operation cost – Formulate defoamer NOT to produce deposits, safe operation instead – In the light of the concept, the least and last consideration is minimization of defoamer dosage. Other benefits are priorized, like:

• Higher solids in black liquor to evaporation ( $$$ energy savings)
• COD Carryover reduction ($$$ chlorine dioxide reduction)

Background Mill Results

Mill case A

• Typical kraft pulp mill, earlier optimized for lowest possible defoamer unit cost.
• Periodical issues with kappa variation,
• Production disturbances with abrupt stops of varying periods.
• We identified the BSW was “too optimized” chemistry-wise,
• We switched current silicone defoamer to another one with more robust

chemistry,

• Applied new dosing points alongside the existing old ones, and increased the

total dosage with higher defoamer unit cost as such.

• In turn, the impact on total cost and productivity was remarkable.

Mill case A Conductivity Reduction

BL dry solids increase

Less stops on BSW and higher net production

Background Mill Results

Mill case B

• Case B highlights another brown stock washing plant.
• Improvement done by increasing drainage rate of filtrates through the washer

by using proper silicone defoamer with drainage effects.

• Regular defoamer product without said effect was replaced.
• “Mill B” bleaching operation was influenced positively by cleaner pulp

entering first bleaching plant stage.

• Higher BSW efficiency was possible by higher drainage rate through the

washer and presses.

• Evidence of this effect was showed by higher vacuum rates through deckers,

with improved discharge.

• When trial stopped decker vacuum reduced instead.
• Wash press operations were also benefited by higher drainage effects

through BSW.

Background Mill Results

Mill case B ( cont.)

• Overall BSW efficiency improvement resulted in 10 to 15% lower conductivity

in pulp carried out to bleaching plant.

• Savings in first month operation achieved an average of 1,0 kg ClO2 / ADT,

measured as chlorine dioxide.

• These savings would pay out several times cost of silicone defoamer as

washing aids.

Background Mill Results

Mill case B ( cont.)

• 35
• 30
• 25
• 20
• 15
• 10
• 5

50 100 150 200 250 300 350 400

bar

Data

Decker Vacuum

Reference Transition Trial Post Trial Post Trial

5000 10000 15000 20000 25000 50 100 150 200 250 300 350 400

µS/cm

Data

Conductivity Press #1

Reference Transition Trial Post Trial Post Trial

Vacuum increase and conductivity reduction

Background Mill Results

Mill case B

10 12 14 16 18 20 22 24 50 100 150 200 250 300 350 400

ClO2, kg/ADT Data

Total Chlorine Dioxide

Reference Transition Trial Post Trial Post Trial Chlorined dioxide reduction

Results and Discussion

Mill case C

• It’s is a Brazilian eucalyptus kraft pulp mill, with conventional washing plant.
• Brown stock washing improvement also by increasing drainage rate of

filtrates through the washers by using proper silicone defoamer and washing aid formulated in same product with drainage effects,.

• Regular silicone defoamer product was replaced.
• Relative mill production on percent of production targets for reference and

trial periods, both periods were on same level of 97% of target production, and dilution factor profile on same level.

• Trial results were divided into two periods because second part of trial was

done with significant increase on carryover from digester (Alkaline loss and COD), due to limitations on extraction screen in digester not related to trial.

Results and Discussion

Mill case C

40 60 80 100 100 200 300 400 500 600 700 800 900 10001100120013001400

% of Production Target Data

Relative Production Level vs Target

Reference Period Trial Period 1 Trial Period 2

0,0 0,5 1,0 1,5 2,0 2,5 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

m3/ADT

Data

Dilution Factor

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case C

• 0,35
• 0,30
• 0,25
• 0,20
• 0,15
• 0,10
• 0,05

0,00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Bar Data

Vacuum Washer Filters

Washer #1 Washer #2 Average Ref. Washer #1 Average Ref. Washer #2

Results and Discussion

Mill case C

12 13 14 15 16 17 18 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

%

Data

Vaccum Filters Discharge Consistency

Reference Period Trial Period 1 Trial Period 2

2 4 6 8 10 12 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

%

Data

Valve Opening for Consistency Control to Reactor

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case C

300 350 400 450 500 550 600 650 700 100 200 300 400 500 600 700 800 900 10001100120013001400

kg Na2SO4/t pulp Data

Alkaline Carryover from Digester

Reference Period Trial Period 1 Trial Period 2

200 300 400 500 600 700 100 200 300 400 500 600 700 800 900 10001100120013001400

kg Na2SO4/t pulp Data

Total Alkaline Carryover Removal on BSW Plant

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case C

550 600 650 700 750 800 850 900 950 100 200 300 400 500 600 700 800 900 10001100120013001400

Kg O2/t pulp Data

COD Carry Over from Digester

Reference Period Trial Period 1 Trial Period 2

8 10 12 14 16 18 20 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

kg O2/t pulp

Data

Pulp COD to Bleaching

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case C

1,5 1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3 2,4 2,5 100 200 300 400 500 600 700 800 900 10001100120013001400

kg Act Chlorine / ADT per Kappa Unit

Data

Kappa Factor First Stage

Reference Period Trial Period 1 Trial Period 2

20,0 22,5 25,0 27,5 30,0 32,5 35,0 37,5 40,0 42,5 45,0 100 200 300 400 500 600 700 800 900 10001100120013001400

kg Act Cl2 / ADT

Data

Total Chlorine Dioxide

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case C

89,0 89,5 90,0 90,5 91,0 100 200 300 400 500 600 700 800 900 10001100120013001400

%ISO

Data

Final Brightness on Bleaching Plant

Reference Period Trial Period 1 Trial Period 2

0,0 2,0 4,0 6,0 8,0 10,0 12,0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

kg / ADT

Data

Total Hydrogen Peroxide

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case C

8 10 12 14 16 18 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

kg / ADT

Data

Caustic Soda on Bleaching

Reference Period Trial Period 1 Trial Period 2

4 6 8 10 12 14 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

kg / ADT Data

Total Sulfuric Acid

Reference Period Trial Period 1 Trial Period 2

Results and Discussion

Mill case D

• Mill case D is a Brazilian eucalyptus kraft pulp mill,
• Modern pressure washers.
• Achieved brown stock washing improvement by increasing drainage rate of

filtrates through the washer by using proper silicone defoamer and washing aid with drainage effects in same product.

• A regular silicone defoamer product was replaced.

Results and Discussion

Mill case D

90 92 94 96 98 100 102 100 200 300 400 500 600 700 800 900 1000 1100 1200

% Data

Relative Production Level vs Target

Reference Period Trial Period

Results and Discussion

Mill case D

600 700 800 900 1000 1100 1200 100 200 300 400 500 600 700 800 900 1000 1100 1200

kgO2/t Data

COD Carryover from Digester

Reference Period Trial Period

Results and Discussion

Mill case D

70 90 110 130 150 170 190 210 100 200 300 400 500 600 700 800 900 1000 1100 1200

kgO2/t Data

COD Carryover to O2 Delignification

Trial Period Reference Period

6 8 10 12 14 16 18 20 22 24 26 100 200 300 400 500 600 700 800 900 1000 1100 1200

kgO2/t Data

COD Carryover to Bleaching

Trial Period Reference Period

Results and Discussion

Mill case D

1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 100 200 300 400 500 600 700 800 900 1000 1100 1200

m3/ADT Data

Dilution Factor

Trial Period Reference Period

Results and Discussion

Mill case D

2,1 0,2 10,0% 1,9 0,2 12,9%

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

Average Std VC

m3/ADT

Dilution Factor

Reference Period Trial Period

Conclusions

Mill trials demonstrate: – There is further potential to chemistry-wise unlock higher productivity in brownstock washing area which has reached machinery-wise the limits of capacity. – Appropriately designed state-of-art silicone defoamer can successfully serve as washing aid to elevate washing performance of current BSW equipments. – A revised BSW chemistry, even with higher dosage and unit cost, can translate into significant payback in bleaching and recovery costs without compromising pulp quality.

Conclusions

However, it requires a decision making by switch from defoamer unit cost minimization to total cost savings perspective with following guidelines:

• Focus on improving process stability
• Designing robust chemistry with state-of-art wash aids
• Instead of unit cost, focus on total operational cost reduction
• High-quality formulated products to avoid carry-over, guarantee safe
• peration instead

References

• Pikka, O., Vesala, R., Carlsson, J. G., Steffes, F., Gullichsen, J., Pulp washing applications.

In: Chemical Pulping (Ed: Papermaking Science and Technology series), ISBN 952-5216- 06-03, Fapet Oy, Finland, pp. 573-601, (2000).

• Kopra, R., Application of the refractometer in the measurement and monitoring of brown

stock washing, Doctoral Thesis, MKKK, Finland, (2015).

• Garret, P.R., ed. (1992). "3". Defoaming. Theory and Industrial Applications. Surfactant

Science Series 45. CRC Press. pp. 151-175. ISBN 0-8247-8770-6.

• Ala-Kaila, K., Modeling of mass transfer phenomena in pulp-water suspensions. Doctoral

Thesis, Helsinki University of Technology, Helsinki, Finland, ISBN 952-5148-70-

• Perking, J. K, How to improve kraft brown stock washing efficiency. Paper Trade Journal, v.

153(8), p. 30-34, (1969).

• Rogers, J., Funo, P.K., Nery, J. ,A lavagem da polpa. São Paulo: ABTCP Conf.(1995).
• Bryntesson, J., Dahlöff, H., Petterson, E. A. K., Ragnar, M., New concept technology for

washing of chemical pulp. Proceedings African Pulp and Paper Week, Durban, (2002)

• Tappi Standard Procedures. Tappi Press. Atlanta, USA.

Acknowledgements

Kind support provided by pulp mill personnel for providing data, Nopco Paper Technology and Mathiesen Group for support this paper and experts from both companies for helping to write the paper are greatly appreciated.

THANK YOU ! Questions welcome

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