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Membrane filtration for water reuse in pulp and paper industry

Acqueau, March 12th 2015

Hanna Kyllönen*, Pauliina Tukiainen* and Pasi

Nurminen**

* VTT Technical Research Centre of Finland

** Valmet

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Water purification and reuseWater intensive industries

Water in pulp and paper industry

Use of water:

– Process water (paper making, pulping)

– Water for showers (wetting, trimming, cleaning, cooling, antifoam)

– Cooling

– Boilers (steam production)

– Sealing

– Cleaning

A lot sufficiently clean water is used by counter-current principle

Effluent treatment usually in waste water treatment plant

– High in suspended solids (SS) and organic matter

– Increased BOD (biological oxygen demand) or COD (chemical oxygen demand)

loadings, as well as organic pollutants, require biological treatment

– Tertiary treatment is required for mills with high inorganic loadings or non-

biodegradable matter

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Low fresh water consumptionDriving forces

Environmental aspects:

– Environmental load will be lower

– Limitations at effluent emissions and water amounts

Water costs

– Fresh water and effluent water

Energy cost

– Water transport energy and heat out from the process

Water treatment capacity too low

– Internal water recirculation give reserves to fresh water treatment and effluent

treatment

Good water management improves runnability and quality of products

at paper machine (PM)

Green image

Benefits for runnability and efficiency

Continuous removal of bacteria, solids and colloids

from water used at PM has several benefits:

– Less slime problems

– Less clogging problems

– Cleaner machine

– Better drainage properties

– Better paper machine runnability

– Better paper quality

– Lower wet end chemical consumption and costs

– Less energy

Recommendation by Valmet e.g for PM white water

to ensure good PM runnability on recycled fibre

OCC based liner/fluting line:– COD < 5000-7000 ppm

– Ca < 500 ppm

– Cl < 300 ppm

– SO4 < 500 ppm

– Bacteria < 106 cfu/ml

– Conductivity < 5 mS/cm

– pH > 6.55

Membrane filtration as a part of water purification

Pre-treatment:

•Filtration (sand, MF)

•Sedimentation

•Flotation

•Biological treatments

•Chemical treatments

Conventional

membrane treatment:

•Ultrafiltration (UF)

•Nanofiltration (NF)

•Reverse osmosis (RO)

Post-treatment:

•Oxidation

•Chemicals

•UV

•Cavitation

Feed

Purified water

Steps to controlled water management in P&PFresh water consumption m³/ton of paper

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All fresh water to paper machine

Counter-current principle for all process water

Waste water out from pulp mill

Separate water loops for different departments

White water treatment /microflotationRecycling and cleaning of save all clear filtrates

Minimizing the long loop water volume Biokidneys for pulp mill

Salt removal with OptiFilter NF

Efficient pulp washing before paper machine

Water buffer volume bigger than stock volume

Effluent treatment and microflotation

Removal of stickies and ash/microflotation

White water treatment with OptiCycle W

Extractives removal with OptiCycle R

Recommended Actions ValmetTechnologies

15 m³/t

10 m³/t

5 m³/t

0 m³/t

20 m³/t

All make up water from clean to dirty

Stable process conditions; no temperature or pH variations

Minimizing the salts at chemicals and process

8 m³/t

Separation ranges for membrane technology

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0,001 0,01 0,1 1,0 10 100 1 000 10 000g/mol 200 20 000 100 000 500 000

Reverse osmosis

Nanofiltration

Particle Separation

Microflotation

Fibers

Metal ions

Salts

Sugar

Lignans

µm

Typical cut off for OptiCycle W

Microfiltration

Fines

Coating pigments

Bacteria

Sizing agent

Fillers

Colloidal pitch

OptiCycle W Ultrafiltration

Poly and oligo saccharides

Lignins

Starch

Latex and binders

Virus

Cross flow membrane filtration

Membrane filtration is based on continuous cross flow filtration, which

is the main key for successful filtration process

– prevents particles from penetrating membranes pores

– the higher the cross flow velocity, the better turbulence and capacity

– cross flow usually created with flow velocity, typically 3 – 5 m/s

– in OptiFilter CR cross flow is created with rotors >10 m/s

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White water treatment for paper machineQuality improvement with OptiCycle W

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- Wire section high pressure

and low pressure showers

- Wet end chemicals

- Sealing waters

- Pulp dilutions

- PM low pressure showers

OptiCycle W -

Ultrafiltration PermeateClear Filtrate

Feed to OptiCycle W

Concentrate to

waste water treatment

Research case – OCC drainage properties

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Reused water should not cause

problems but should fulfil the

requirements for drainage and thereby

runnability

In the research membrane filtration was

used to produce good quality water for

reuse in OCC mill

– Lab scale OptiFilter CR250 using

membranes with cut off of 30 kDa (UF)

– The use of filtrated water for reuse gave in

all the cases better drainage results for

OCC pulp than waters with no UF

– The drainage times were the shortest when

membrane filtered waters were used.

OptiFilter CRModel

OptiFilter CR 1010/100

membrane area 140 m²

membrane diameter 1000 mm

filter cassettes 100 pcs

motor 110 kW

weight, ca 9 900 kg

size, ca 4,3 x 1,4 x 2,4 m(height - width - length)

membrane pore size 0.02 µm

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OCC Liner FlutingOptiCycle W capacity - 24 months

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Realized Permeate flow 1500-2000 m³/day (~ 110-150 l/m2h)

Dimensioned flow 1200-1500 m³/day (~ 90-110 l/m2h)

Novel concept: Water reuse by FO for soda ash rinsing and chemical production by ED

Chloride free Na2SO4 with other

multivalent salts back to pulping process

Dilute salt solution e.g. back to rinsing

Solubilized Na2SO4 with

soluble impurities (NaCl, KCl)

Filtration

ESP

dust

Caustic

mixture

Acid

mixture

Dilute BL, hemi, tannin, etc.

Concentrate

Soda

ash

rinsing

FO

ED

Acid soda

salt

pH < 2

In order to devise plans for water reuse

1. Detrimental substances

introduced in the different

circuits.

2. Possible treatments for each

stream.

3. The specifications or water

quality necessary for different

uses in the process.

Water Footprint – potential of

the exercise

System Modeling and lab testing

Measurements and Analysis

Phenomenon Modeling

and pilot testing

Reduction of water consumption without affecting product quality or process.

This will mean significant economic and environmental advantages.

Aspects for water reuse

Further information:

Hanna.kyllonen@vtt.fi

Pasi.nurminen@valmet.fi

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