Pulp and Paper Ind.

8/3/2019 Pulp and Paper Ind.

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by: Marika B. Yamson



Introduction

yPulp is a lignocellulosic fibrous materialprepared by chemically or mechanically separating cellulose fibres from wood, fibrecrops or waste paper.

y W ood pulp is the most common rawmaterial in papermaking.



Introduction

The pulp and paper industry converts wood orrecycled fibre into pulp and primary forms of paper.

In the 1800s, there was a shift away from usingcotton rags for paper production. W ood

became the most important source of fiber. First mechanical and then chemical methods

have been developed to produce pulp from

wood.



Pulp and paper mills

Pulp mills separate the fibres of wood or

from other materials, such as rags, wastepaper or straw in order to create pulp.

Paper mills primarily are engaged inmanufacturing paper from wood pulp andother fibre pulp, and may also manufactureconverted paper products.



Production process

The production process can be divided into 7 sub-processes:

raw materials processes; wood-yard;

fibre line;

chemical recovery;

bleaching;

paper production;

products and recycling.



Simplified flow diagram of

integrated mill



Preparation for pulpingy W oodchipping is the act and industry of chipping

wood for pulp, but also for other processed

wood products and mulch.y Only the heartwood and sapwood are useful for

making pulp.

y Bark contains relatively few useful fibres and is

removed and used as fuel to provide steam for use inthe pulp mill.

y Most pulping processes require that the wood bechipped and screened to provide uniform sized chips.



Pulping processesPulping aims to separate cellulose fibers from the wood

structure.

Possible types of pulp production are:

y Kraft (68%)

y mechanical (22%)

y semi-chemical (4%)

y sulphite (4%)

y dissolving (2%).



Mechanical Pulpy Manufactured grindstones with embedded silicon

carbide or aluminum oxide can be used to grind

small wood logs called "bolts" to make stonegroundwood pulp (SG W ).

y If the wood is steamed prior to grinding it isknown as pressure groundwood pulp (PG W ).

y Most modern mills use chips rather than logs andridged metal discs called refiner plates instead of grindstones.



Mechanical Pulpy If the chips are just ground up with the plates, the

pulp is called refiner mechanical pulp (RMP) and

if the chips are steamed while being refined thepulp is called thermomechanical pulp (TMP).

y Steam treatment significantly reduces the totalenergy needed to make the pulp and decreases the

damage (cutting) to fibres.y Mechanical pulps are used for products that

require less strength, suchas newsprint and paperboards.



Thermomechanical Pulp

yThermomechanical pulp is pulp produced

by processing wood chips using heat(thus thermo) and a mechanical refiningmovement (thus mechanical).

y

It is a two stage process where the logs arefirst stripped of their bark and convertedinto small chips.




yThese chips have a moisture content of

around 25-30% and a mechanical force isapplied to the wood chips in a crushing orgrinding action which generates heat and

water vapour and softens the lignin thusseparating the individual fibres.




yThe pulp is then screened and cleaned, any

clumps of fibre are reprocessed.yThis process gives a high yield of fibre from

the timber (around 95%) and as the lignin

has not been removed, the fibres are hardand rigid



Chemical Pulp

yChemical pulp is produced by combining

wood chips and chemicals in large vesselsknown as digesters where heat and thechemicals break down the lignin, whichbinds the cellulose fibres together, without

seriously degrading the cellulose fibres.



Chemical PulpyChemical pulp is used for materials that

need to be stronger or combined with

mechanical pulps to give a product differentcharacteristics.

yThe kraft process is the dominant chemical

pulping method, with sulfite process beingsecond. Historically soda pulping was thefirst successful chemical pulping method.



Kraft PulpingSulfate or Kraft pulping was invented in Germany in 1884 and remains the dominating technology today.

Advantages:

y higher pulp strength

y wider variety of wood species may be used

y more effective at removing impurities like resins.

Disadvantage:

y the pulp yield is low, less than 50%.



Sulfite Pulpingy Sulfite Pulp. The quantity of pulp made by this

process steadily diminishes despite its high quality,

because of the water pollution problems which itcauses.

y A lthough spruce is the wood most commonly employed, appreciable quantities of hemlock and

balsam are also used.y The wood is barked, cleaned, and chipped as

described for sulfate pulp, the resulting chipsbeing about 1.5 cm in length



Sulfite Pulping

y It is then conveyed to storage bins above the

digesters preparatory to being cooked.yThe usual sulfite process consists of

digestion of the wood in an aqueoussolution containing calcium bisulfite and anexcess of sulfur dioxide.



Sulfite Pulpingy The sulfite process involves two principal types of

reactions, which are probably concurrent:

y Sulfonation and solubilizing of lignin with thebisulfite

y Hydrolytic splitting of the cellulose-lignincomplex.

y The hemicellulose are also hydrolyzed to simplercompounds and the extraneous wood components

acted on.



Sulfite Pulpingy Since disposal of waste liquor (more than half of

the raw material entering the process appears here

as dissolved organic solids) creates a serious waterpollution problem, concerted attention has beenturned to its removal or utilization.

y A slurry of magnesium oxide is substituted forlime, because the chemical and heat recovery arepossible, and a solution t the disposal problem of the waste liquor is also provided.



Sulfite PulpingySodium and ammonia have also been

substituted for calcium as a pulping base in

a limited way.yThe waste liquor from the calcium sulfite

process cannot have its values used over

again, since the calcium sulfite does notdecompose to sulfur dioxide, whereasmagnesium sulfite does.

yCaSO4 is formed and lost.



Sulfite Pulping

y Hence the newer and technically more acceptable

sulfite process is based on magnesium bisulfiterather than the earlier used, correspondingcalcium compound, resulting in a greaterconcentration and more active combined sulfur

dioxide, without dander of precipitation and withquicker separation and solution of thenoncellulose wood constituents (lignin andhemicellulose).



Sulfite PulpingySulfur is melted in a tank heated by the

rotary burner and then fed to the burner foroxidation.

y A ny sulfur that is vaporized in the burnerenters a combustion chamber, where it is

oxidized to sulfur dioxide.yThe amount of air in this operation is closely

controlled to prevent the formation of sulfur

trioxide.



Soda Pulping

ySoda pulping is brought about by a

procedure similar to that used for sulfatepulp, except that the dissolving agent isNaOH/Na2CO3 and the make-up chemicalis Na2CO3 instead of Na2SO4.

y Its importance is too small to warrantadditional details here.



Recycled Pulp

yR ecycled pulp is also called deinked

pulp (DIP).yDIP is recycled paper which has been

processed by chemicals, thus

removing printing inks and other unwantedelements and freed the paper fibres. Theprocess is called deinking.



Recycled PulpyDIP is used as raw material in papermaking.

Many newsprint, toilet paper and facial

tissue grades commonly contain 100%deinked pulp and in many other grades,such as lightweight coated for offset and

printing and writing papers for office andhome use, DIP makes up a substantialproportion of the furnish.



Organsolv Organosolv pulping uses organic solvents at

temperatures above 140 °C

to break downlignin and hemicellulose into solublefragments.

The pulping liquor is easily recovered by distillation.



Alternative Pulping MethodyResearch is under way to develop biological

pulping, similar to chemical pulping but

using certain species of fungi that are able tobreak down the unwanted lignin, but notthe cellulose fibres.

yThis could have major environmentalbenefits in reducing the pollution associated

with chemical pulping.



Alternative Pulping Methody The pulp is bleached using chlorine dioxide stage

followed by neutralization and calcium

hypochlorite.y The oxidizing agent in either case oxidizes and

destroys the dyes formed from the tannins of the wood and accentuated (reinforced) by sulfides

present in it.y Steam exploded fiber is a pulping and extraction

technique that has been applied to wood and otherfibrous organic material.



Bleachingy The pulp produced up to this point in the process

can be bleached to produce a white paper product.

y The chemicals used to bleach pulp have been asource of environmental concern, and recently thepulp industry has been using alternatives

to chlorine, such as chlorinedioxide, oxygen, ozone and hydrogen peroxide.



Environmental problemsRegulated wastes and emissions from the pulp andpaper industry include liquid and solid wastes, air

emissions, and wastewater.

y Air emissions related with this process are: sulphurdioxide, nitrous oxides, particulate matter,

methanol, polycyclic organic matter, hydrogenchloride, formaldehyde, chloroform, phenol andchlorinated phenolics, dioxins, furans and otherchlorinated compounds.



Environmental problems

y W astewater releases include chlorinated

phenolics, dioxins, furans and otherchlorinated compounds, phosphates andsuspended sediments.

yPaper mills also produce non-hazardoussolid waste such as sludge derived fromtheir pulping and bleaching operations.



Raw water usey Pulp mills are big water users. The total requirement

of raw water has through cleaner production

measures been reduced from about 200-300 m3

perton of pulp in 1970 to well below 50 m3/ton, in somemills even below10 m3/ton.

y Consumption of fresh water can seriously harmhabitats near mills, reduce water levels necessary forfish, and change water temperature, a criticalenvironmental factor for fish.



Pollutants in effluentsy The most common organic pollutants are

suspended solids (SS):

y lost cellulose fibre,y dissolved organic compounds such as dissolved

lignin compounds, carbohydrates, starch andhemi-cellulose

y A cidic compounds are predominantly natural resinacids.

y Chlorinated organics ( A OX) are found if elementalchlorine is used in the process.



Solid wastesy Dirty wood chips or fibers as well as bark.

y The broken, low-quality fibres are separated outto become waste sludge.

y

A ll the inks, dyes, coatings, pigments, staples and"stickies" (tape, plastic films, etc.) washed off therecycled fibres.



Energy use

y The pulp and paper industry uses 84% of thefuel energy consumed by the forest productsindustry as a whole.

y It is one of the largest producers of greenhousegas (GHG) emissions.

y Over the past few years, the pulp and paperindustry has considerably reduced its GHGemissions by introducing energy conservationprojects and by increasing its use of biomass asan energy source.



Energy usey A modern kraft pulp mill is essentially self-

sufficient in energy . The only oil consumer is the

causticing oven, which however can be replaced with bio-fuel.

y A paper mill requires between 400 and 1000 k W helectricity/ton paper and 4 8 GJ heat/ton for

drying in the paper machine.

y In an integrated pulp and paper mill this energy isprovided from the recovery boiler.



Cleaner production measures

Raw materials

y Maintaining moisture content of the raw

materials constant all year around.y Keeping chemical inventory to a minimum

and buying small containers of infrequently usedmaterials.

y Labelling storage area for hazardous substances.y Providing spill containment and collection

systems during storage.

y Genetically modifying forest trees.



Genetically modified trees

yLignin is the main wood component thatmust be effectively removed from the pulp.

y It has been possible to use geneticengineering to modify lignin content

and/or composition in poplars.



Advantages of genetic modifications

y Genetic modifications improved characteristics,

allowing easier delignification, using smalleramount of chemicals, while yielding more high-quality pulp.

y Owing to the genetic modification savings inenergy and pollutant chemicals are achieved,thus leading to an environmentally moresustainable process.




Wood-yard

y Pulp mills integrated with lumbering facilities:

acceptable lumber wood is removed duringdebarking; residual or waste wood from lumberprocessing is returned to the chipping process; in-house lumbering rejects can be a significant source

of wood furnish.y A voiding hydraulic debarking saving energy and

water consumption, reducing wastewater amount.




Wood-yard

y Reusing leachate water.

y Co-production from bark: mulch, ground cover,charcoal.

y Burning bark from debarking and small chipsfrom chipping for energy production (depends onthe moisture content).




Pulp productiony Increasing brown stock washing efficiency. A ny

remaining cooking liquor will increase the chemical

consumption in subsequent stages.

y W ater reuse from evaporators. The evaporationplant is always one of the largest steam consumers

in the mill. Condensate might be used instead of fresh water in the mill.

y R epulping the rejects from screening rather than

putting them into the landfill.




Pulp production

y Using pulp centrifuging to remove any remaining

impurities.y Sludge utilization by means of land-spreading.This method of sludge disposal is an area of concern, as sludge constituents are not wellidentified.

y Air emissions control devices.y Providing spill containment and collection

system.




Chemicals recovery

y Using of new technologies (CHP, BLG, heat

transfer, heat exchanger).y Improvements technical parameters of recovery

boiler or furnace (geometrical shape etc.).

y Using light gas strippers and gas collection

systems which will remove hazardous and foulsmelling pollution from the air and increase workplace safety.




Chemicals recovery

yDeaerator tanks ahead of the boilers

to help reduce the intake of freshwater.

y Air emissions control devices.

yProviding spill containment andcollection system.




Bleaching

y A voiding chlorine bleaching.

yContinuing research on biotechnologicalbleaching and electrochemical bleaching.

y A ir emissions control devices.

yProviding spill containment and collectionsystems.




Paper production

y Cleaning the roll in the paper machines toavoid broken paper line.

y Adjustment of edge cutter to reduce sidetrimming loss.

y Use of soft water as a boiler feed water.

y R ecycling water evaporated from drying process

by condensing.




Paper production

yOptimizing the thermal effects on water used

in the paper machine and stock preparation area.

y Providing disk save-all for paper machine.

y R epulping rejected paper in a closed loopmanner.




Products processes and recycling

y Increasing recycling rates. Recycling reduces

energy consumption, decreases combustion andlandfill emissions, and decreases the amount of carbon dioxide in the atmosphere. This processalso saves money.

y Possibility for easy packaging recycling.

y Using green fuel for transportation.



RecyclingIn Europe an average of 56% of used paper isrecovered. The recycling process includesfollowing stages:

y Sorting

y Dissolving

y De inkingy Mixing

y Papermaking process



Ideal paper mill

y From cleaner production point of view is achlorine-free and zero-discharge one, withminimized quantity and toxicity of air pollutionand solid wastes.

y It is seen that closed loops represent the mosteffective approach to save both energy andresource consumption and at the same way todecrease all kind of wastes production.



Ideal paper mill

y Such an approach is developed in the form of paper recycling, different types of substances re-use during production processes, co-productionand chemicals recovery.

y Future research can develop more sustainablereuse options for kraft pulping solid wastes, as well as pulping methods that result in purifiedby-products that can serve as feedstock for othermanufacturing processes.



The EnD!!!

Pulp and Paper Ind.

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