~-

I DEINKING I

Application ofPerformance

ConventionalFatty

Collectors for NewsprintFlotation Deinking

& EnhancedAcid Based Soap

Applications in

Pattabhiraman N.•

ABSTRACT

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The first flotation de inking of German design was started in earlyeighties in India. Today the installed de inking capacity is aroundJ 500 tpd with capacity of detnking varying from 20 tpd to 200tpd. Many of the latest versions of de inking cells of Europeandesigns find their presence in India. More deinktng units arelikely to start in the years to come. Since the use have been moreon the application of newsprint, the article mainly focuses on theprime deinktng chemical of fatty acid based soaps of conventionaland high performance widely used in Europe and to some extentin India. Various other process conditions and variables arebriefly dealt with based in lab testing and field application. Briefcomparison is also made with the uses of synthetic surfactants andother liqutd combinations.

INTRODUCTION gain, yield, and newsprint machine runnability aretaken into account.

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For more than forty years, Europe is using fattyacid based conventional Sodium soaps in theflotation deinking plants. Particularly in the last twodecades. there have been many advances in deinkingequipment as well. These development have resultedin more efficient deinking processes.

In North "<merica and Asia Surfactant baseddeinking chemicals have gained acceptance.However, European Mills in general use greaterpercentage of recycled fibre in the stock to thenewsprint machine, compared to the North AmericanMills. Several European Mills are now running with

While Surfactant based deinking chemicals areavailable, they have not displaced fatty acid basedsoaps to a great degree in Europe. This is Siddha Sri Enterprisesparticularly true for the large volume deinking ofrecycled Newsprint where Soaps have maintained a 15/9, Vijayalakshmi Apartmentspre-eminent position till date because they give a Bharathi Park, Main Road,better performance when factors such as brightness Coimbatore- 641 043 (T.N.)

IPPTA Vol. 13,No.3, Sept. 2001 79

100% recycled fibre on the newsprint machine.

The recent installations of several largenewsprint recycling mills in the far East running with100% recycled fibre on the paper machine hasinitiated a move towards fatty acid soap in Asia.Fatty acid Soaps appear to predominate where highlevels of recycled fibre are used on the newsprintmachine.

European newsprint furnishes have.traditionally contained a very large proportion ofMagazines. Typical furnishes have containedbetween 30 to 50% magazine with newsprint oftenless than three months old providing the rest of thefurnish. Ten years ago, major proportions of anewsprint mill's waste paper come from print houseover issues and returns.

Today more and more of furnish is postconsumer waste. Post consumer waste is generallyrecognized as inferior in quality to print house overissue with variations in the amount of magazines andthe age of the newsprint. The increasing. use of postconsumer waste represents a gradual deterioration ofwaste paper quality. With the increasing utilisationrates and poor collection rates, decreasing quality ofwaste paper supplies is a trend likely to continue.

SOAP SOLUTION PREPARATION

The conventional deinking soaps are either inthe form of solid Needles or in the form of Pellets.Where as the Enhanced performance soap isgenerally in the form of Pellets. To ensure gooddissolution of these soap Pellets in the batchoperated high consistency pulpersof 12 to 15%consistency, the pellets are dosed in the pulper oncethe hot water of around 45 deg. C is taken in thePulper but before feeding the waste paper in thePulper.

Alternatively, a low cost manual or semi-automatic tailor made soap solution preparationarrangement can be made in the deinking plant itself.The requirements are-an elevated dissolving Tank ofaround 2 cubic metre capacity with a standard topmounted propeller/agitator for making a soapsolution at a concentrations of around 50 to 100gpl.a Service tank (with out an agitator) to hold the soapsolution for minimum 8 hours shift, a Metering pumpwith pipe line provision to feed the soap solution in

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I DEINKING Ithe batch or continuous pulper.

The dissolution of the Pellets in the dissolvingtank can be made by steam heating of water to 60-65deg.C. Fluidity of the soap solution is essential without gel formation for which insulation of thepipelines may be needed. We also recommend fittingof a manual valve in the service pipe line so that theline can be flushed with hot water 'or steam if forsome reason the plant is shut for prolonged periodsand there is a possibility of the liquid soap in thepipe line gelling. Some mills prefer to run this sectionat concentrations lower than 50gpl of soapdepending on the plant convenience and theavailable size of the metering pump.

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Such soap solution arrangement also enablesthe deinking plant to have the flexibility to dose thedeinking liquid collectors to (a) full dosing at Pulperor (b) at the cell feed pump or (c) split dosing atpulper and the DI cell of first loop or in the secondloop.

PERFORMANCE CHARACTERISTICSOF CONVENTIONAL I ENHANCED PER-FORMANCE SOAPS AND SYNTHETICSURFACTANTS

This fatty acid based Soap collectors in generaltend to be,

(a) Moderate foaming with very consistentstable foam

(b) Very good in terms of Yield of finished pulp

(c) Relatively low water clarification costs,

(d) . Moderate foam even at higher dosages, needreduced requirement of foam suppressants.Cleaner deinking circuit. stock preparationand paper machine areas.

(e) The soaps offer gentle action on ink andstickies and allows skimming of the buoyanttype stickies efficiently from the cell due tomore agglomeration.

(f) It gives good gain of Brightness across thecells & there by higher extraction of the inkparticles out of the system.

IPPTA Vol. 13,No. 3, Sept. 2001

(g) Soaps offer the possible savings in furnishcosts or in some cases reduced postBleaching costs for highly printed wastes

Yield is a major consideration for largenewsprint mills with a very high daily throughput.For example, yield is a major criterion at one of thebiggest newsprint mills in Europe and even 1 or 2%increase in yield is a significant increase in terms ofannual out put, Admittedly this may not consideredso significant in smaller newsprint units of India.

•On the other hand, with pure Synthetic

surfactants the dosages are very much low. Thedisadvantage with synthetic surfactants generallyused to be,

(a) high foaming levels and the need to controlsuch foam - often requiring the use ofincreased levels of foam suppressants oranti-foams

(b) Possibly significantly lower final yieldsbecause of increased foaming and increasedremoval of ash, fibres and fines.

,(c) Possibly increased cost of water clarification

chemicals.

(d) But even at these dosages, the actions ofsynthetic surfactants on ink is aggressiveand disperse particles in smaller sizes thanwould be the case with soaps which can leadto small particles being re-circulated in thewater circuit.

(e) Synthetic surfactants makes less gainsduring flotation than soap based productsbut make up for this during washing stages,at the cost of yield loss and grayness over aperiod of time.

However Synthetic surfactants at lower dosagelevels are still in use if the above points are notconsidered as significant in a particular millconfiguration. In Indian newsprint units, the dosagelevels of synthetic surfactants vary from 0.20 kg/mt.to 0.8 kg/mt (or maximum 1 kg/mt) of input waste.

However in systems having 'per and postflotation, the synthetic surfactant is also dosed inthe post flotation for simple control of overall

IPPTA Vol. 13, No.3, Sept. 2001

brightness gain and for speck removal.

In some cases surfactants are used as synergistto soap collectors or as foam boosters. In case ofwhite grade application and Tissue deinking units.they are used as low cost solution for Neutral or semineural systems.

The moderate foaming of soaps and itspotential for obtaining high gains across theflotation unit has also paved way for manydevelopments with the deinking chemical suppliersfor single product blend of Fatty acid/synthetic inoptimal ratio in liquid form or two componentchemicals supplied separately.

IMPORTANCE OF LEVEL CONTROLSAND OPTIMUM CONSISTENCY IN THEFLOTATION CELLS

It should be understood that all the inksdislodged/dispersed in the pre deinking area is to beextracted out of the cell with high efficiency. The inkknows only two routes- one to be extracted as scumout of the system or carried with the accepted pulpand be in the system or even carried to the mahcineareas.

Some mills in India are used to high foam levelsfor having used high foaming deinking chemicals.High quantum of foam is not the criteria for effectivedeinking in the cell and in fact the European. de-inkers look for consistent & moderate foamingdeinking chemical which is stable in quality withoutcollapsing with the ink. Hence in such cases of soapbased collectors, the level of the stock in the cell hasto be kept at a higher level than adopted for highfoaming products. Lack of calcium results in smallerbubbles and makes the setting of the flotation cellsmore difficult.

There is one rule that must be observed. Inflotation machines having secondary cells forhandling the rejects of the primary, the accepts ofthe secondary cell going back through the flotationsystem must be at least 3 to 4 points higher inbrightness compared to the feed stock brightness.Accordingly the cell operation has to be adjusted.The mills in fact. has to compromise with thesecondary cell- between rejects rate and brightnessattainment.

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At 0.9 to I% feed consistency of the cells goodresults in terms of brightness and speck reduction isobtained. This is applicable to all designs of cells.For want of proper thickening unit after the cells, themills are forced to operate the cells at highconsistencies due to limitations in the hydrauliccapacity of the thickeners.

SYSTEM DESIGN AND ITS IMPACT ONDEINKING PERFORMANCE

Thickener type : Some mills have highefficiency double nip filters after the flotationmachine as thickeners. These units may be of highutility value for the white grades of papers or fortissues. For market reasons when the deinking unit isto be operated with the same flow sequence fornewsprint manufacture, then high washing unitsextract the high brightness fillers and fines leading tovery high load on clarification units and ultimately tolow yields. The performance of the cells gets verymuch disturbed because of the same. For newsprintapplications efficient Disc filters are in regular usedin Europe.

Post flotation and Post bleaching : Excepta couple of mills. all other operating deinking unitsin India still have only pulper bleaching withhydrogen peroxide. If high gains between the Pulper& the complete deinking street is foreseen, then postbleaching with down ward flow Hydrogen peroxidebleaching followed by a well designed up ward flowSodium hydro sulphite bleaching is a must, with anin between dispersion and post flotation units.

Filtrate water clarification : Gradual buildup of various disturbing elements. ink particles in thedeinking circuit take place, when the system is madefully closed with out any clarification of thethickener filtrate. The disturbing elements if notextracted out of the system will find the way to thenewsprint machine affecting the quality and/or thesteady performacne and runnbility of the machine.Depending on the process sequence. partialclarification of the filtrate of the thickener issuggested.

Difficulties in the use of FlexographicPrinted inks in flotation : The flexo printingprocess is a form of letterpress printing using a softplate-printing cylinder. Flexo inks are known as water

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I DEINKING Ibased inks, as the inks binders employed are water-soluble. Papers printed with flexo inks have thereputation of poor deinking because a) the very fineflexo inks are difficult to float from fibre suspensionb) while flexo inks can be removed by washing, itusually results in high losses.

To identify the content of flexo ink in aparticular newsprint waste, the waste paper is pulpedin a lab. pulper then diluted and filtered through afilter paper in a Buckman type filter funnel. Thefiltrate passing through the pad is to be observed. Ifit is only slightly grey then the waste paper is notflexographicaly printed. If the filtrate water is verydark it is almost certainly flexographic print. Theserelics on the fact that flexo-graphic ink particles arevery small (below one micron) they tend to washthough the filter pad more than conventional inks.Flexo ink always lowers the starting brightness in thepulper. The best way is to avoid using the flexo-printed wastes, though there are some developmentsto use them in small quantities by means of speciallydesinged flotators in the filtrate circuit.

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In the following pages we are placing thecomparative findings of SERF AX Soaps in newsprintapplications for flotation deinking: ••

COMPARATIVE FINDINGS OF SERFAXSOAPS IN NEWSPRINT APPLICATIONSOF FLOTATION DEINKING

SERFAX deinking Soaps of StephensonRecycling Chemicals, Bradford. UK has been used indeinking applications for over 20 years. During thisperiod Stephenson personnel have had plenty of timeto establish the best possible working conditions forSERF AX soaps.

This short report shows how the followingbasic factors effect the efficiency of flotation usinga newsprint based furnish.

• Water hardness

• Flotation cell pH

• Magazine content

• Application rate

IPPTA Vol. 13,No. 3, Sept. 2001

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STANDARD CONDITIONS

All the results contained in this report comefrom laboratory trials. In these trials standardconditions were used unless otherwise stated.

Standard conditions were•

Furnish

• 70:30 news/magazine (European origin)

Pulping (Lamort Deinkit) Chemicals

Consistency = 12% Sodium Silicate(30° Baume = 2.0%

Duration = 15 minutes Peroxide (as 100%active) = 1.0%

Temperature = 50°C Caustic to pH = 10.5

Flotation (Lamort deinkit) Chemicals

• Consistency - 1.0% CaCl2 to 220 ppm asCaCO) (12°0)

Duration = 8 minutes SERFAX Soap

Temperature = 45°C

Unless stated Enhanced performance SoapSERFAX-OBE was dosed at 0.6% on fibre andConventional deinking Soap- SERFAX mt90 wasdosed at 0.8% on fibre. In the following findingsmt90 represents the conventional deinking soap andDBE represent the High Performance deinkingsoapsof SERF AX.

FINDINGS•

1) Effect of Calcium hardness on brightnessgain

The graph no. 1 shows that the highPerformance deinking soap-SERFAX DBE is moreresilient to lower water hardness levels as at theselower levels it gives better brightness results thanthe conventional deinking soap- SERFAX mt90.

IPPTA Vol. 13, No.3, Sept. 2001

The graph also shows that Calcium hardnessdoes influence brightness gain and that an optimumhardness is between 200 to 250 ppm as CalciumCarbonate. 12-15°0)

The calcium requirement is usually met byeither the furnish, where Calcium Carbonate coatedmagazines are added or by the natural water supply .

Graph 1: EFFECT OF CALCIUMHARDNESS ON BRIGHTNESS GAIN

50 100 150 2DO 250 300 350

HIInI••• _ JIIIIIIc.Ic:iI. ~

Graph 2: Brightness Gain as a function offlotation cell pH

14

12

10

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2

7 U • U • U 10 1U ~

•••••••••••••

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If calcium levels are low « 200 ppm) CalciumChloride can be added either as a saturated solution(Usually w/w 35% solids) to the flotation cells or assolid flakes to the pulper).

2) Brightness gain versus pH

'.The graph no. 2 shows the brightness gain

achieved as a function of laboratory flotation cell pHfor both SERFAX soaps.

I DEINKING Isoap converts to the fatty acid species and thatbelow a pH of 8.0 the conversion to the fatty acidspecies is very quick.

3) Flotation cell consistency

The graph no. 3 below shows the effectlaboratory flotation cell consistency has onbrightness gain when using any of the SERF AXsoaps.

The graph shows that the optimum pH for both The graph shows that increasing the flotationSERFAX soaps is pH = 8.5 however a range of cell consistency above 1.2% has a negative effect onbetween 8.0 to 9.0 is usually advocated. brightness gain efficiency.

Calcium soaps exist in equilibrium dictated bypH. At alkaline pH the sopas are present mainly asthe Calcium soaps, necessary for effective deinking.At acid pH the soaps converts back to their fattyacid form. At intermediate .pH the fatty acid and soapcoexist. Control of pH is therefore important to avoidor resolve potential problems.

If the pH becomes too high then alkalineyellowing takes place, which causes the brightnessto drop.

If the pH becomes too low then the deinkingsoap may revert back to the fatty acid and henceflotation will be compromised. As the pH falls the

Graph 3: Flotation consistency versusbrightness gain

14

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12.1

t

I12

11.1

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OJI OJI 1.2 1.4 ,.. 1.11 2• •••••• ncr

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The graph was derived using a SERFAX soapof MT90 and DBE however the same relationshipholds for most other deinking chemicals.

4) Magazine content versus brightness gain

The graph no. 4 below shows the relationshipbetween increasing magazine content and brightnessgain. (The rest of the furnish was made up of overissue newsprint of UK origin).

The largest increase in brightness gain can beseen when going from 20% to 30% magazine.

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It is for this reason that a 70% newsprint 300/.magazine furnish is usually recommended fOI

Graph 4: Magazine content versusbrightness gain for SERFAX soaps

o ~ ~ ~ ~ ~ a ~ i S ~"•.•..•..•.•........

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Graph 5: Soap application rate versusbrightness gain

14

13

12

Ir10

• ••7

~~

0.2 0.4 0.8 0.8

~_CIIII_

1.2

optimum brightness results in the deinking plant asit gives in most cases the best compromise betweenperformance and cost.

•The graph also shows that high Performance

SERF AX DBE soap gives better results than theconventional SERFAX MT90 soap at lower magazinelevels.

Graph 6: Solubility times for SERF AXMT90 and DBE (5 and 10%

Concentrations)

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IPPTA Vol. 13, No.3, Sept. 2001.

5) Optimum application rates

The graph no. 5 shows that conventionaldeinking soap of SERF AX MT90 reaches an optimumapplication rate at 0.8% on fibre but the highperformance SERFAX DBE soap reaches an optimumapplication rate at 0.6% on fibre.

6) Solubility times for SERFAX soaps (5%and 10%. solutions)

The graph no. 6 shows the solubility times forboth conventional and high performance soaps ofSERFAX DBE & SERF AX MT90. It can be seen thatas the temperature of water increases the timeneeded to dissolve the soap decreases.

OBSERVATIONS

The report shows that the main differencebetween high performance SERF AX DBE andconventional SERF AX MT90 is in the addition rateas laboratory results shows a lower addition rate canbe used with SERF AX DBE with no loss inperformance.

Also high performance SERFAX bBE soapcontains a small percentage of synthetic additives,which allow the product to generate more foam thanSERFAX MT90. This we believe explains the slightlybetter results with high performance SERFAX DBEat lower hardness and with lower magazine contentfurnishes.

CONCLUSIONS

For deinking plants running with "idealconditions" in terms of water hardness and magazinecontent we would recommend conventionalSERFAX MT90 soap as the preferred dcinkingchemical for use in that plant.

For plants using low magazine contentfurnishes and or with low water hardness we wouldrecommend high performance SERF AX DBE as thepreferred deinking chemical.

ADDITIONAL COMMENTS

This report is intended as a guide for working

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with the conventional and high performance soaps ofSERFAX MT90 and DBE.

It should be noted however that every deinkingplant is different and that deinking chemicals shouldbe optimised separately for each plant.

Although the report shows the best possibleconditions for SERF AX soaps it should be noted thatthey would work in a variety of deinking applicationsunder a wide range of conditions.

It should however be stated that all plants aredifferent and application rates will vary and can

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I DEINKING Ioften be reduced after the start up period. Everydeinking plant operates in a unique way. Even twoplants built to the same design are likely to yielddifferent results - reflecting the complex relationshipaffecting deinking efficiency. Factors that influecnede-inking performance include Furnish, Pulping, Inktype, Printing process, Reagents, Equipment. Waterquality, Process control. Economics, Environmentetc.

The author thanks Stephenson RecyclingChemicals, Bradford UK for having permitted to partwith their comparative testing of conventionaland high performance soaps for newsprintapplications.

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IPPTA Vol. 13, No.3, Sept. 2001