lec 7- pulp and paper industry (f)

8/8/2019 Lec 7- Pulp and Paper Industry (F)

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Waste waster treatment inPulp and paper industry

www.forestproducts.sca.com


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Introduction

The pulp and paper industry converts wood or

recycled fibre into pulp and primary forms ofpaper.

In the 1800s, there was a shift away from using

cotton rags for paper production. Wood became

the most important source of fiber.

First mechanical and then chemical methods

have been developed to produce pulp from

wood.


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Pulp and paper mills

Pulp mills separate the fibres of wood or from

other materials, such as rags, wastepaper orstraw in order to create pulp.

Paper mills primarily are engaged in

manufacturing paper from wood pulp and otherfibre pulp, and may also manufacture converted

paper products.


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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.


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Simplified flow diagram of

integrated mill


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Pulping processes

Pulping aims to separate cellulose fibers from

the wood structure.Possible types of pulp production are:

Kraft (68%)

mech

anical (22%) semi-chemical (4%)

sulphite (4%)

dissolving (2%).www.handprint.com


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Kraft Pulping

Sulfate or Kraft pulping was invented in

Germany in 1884 and remains the dominatingtechnology today.

Advantages: higher pulp strength

wider variety of wood species may be used more effective at removing impurities like resins.

Disadvantage:

the pulp yield is low, less t

han 50%.


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Environmental problems (1)

Regulated wastes and emissions from the pulp

and paper industry include liquid and solidwastes, air emissions, and wastewater.

Air emissions related with this process are:sulphur dioxide, nitrous oxides, particulate

matter, methanol, polycyclic organic matter,hydrogen chloride, formaldehyde, chloroform,phenol and chlorinated phenolics, dioxins,furans and other chlorinated compounds.


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Environmental problems (2)

Wastewater releases include chlorinated

phenolics, dioxins, furans and other chlorinatedcompounds, phosphates and suspended

sediments.

Paper mills also produce non-hazardous solidwaste such as sludge derived from theirpulping and bleaching operations.


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Raw water use

Pulp mills are big water users. The total

requirement of raw waterh

as th

rough

cleanerproduction measures been reduced from about200-300 m3 per ton of pulp in 1970 to well below50 m3/ton, in some mills even below10 m3/ton.

Consumption of fresh water can seriously harmhabitats near mills, reduce water levelsnecessary for fish, and change watertemperature, a critical environmental factor for

fish.


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Pollutants in effluents

The most common organic pollutants are

suspended solids (SS): lost cellulose fibre,

dissolved organic compounds such as dissolvedlignin compounds, carbohydrates, starch andhemi-cellulose

Acidic compounds are predominantly naturalresin acids.

Chlorinated organics (AOX) are found ifelemental chlorine is used in the process.


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Wastewater flowSCA Forest Products, strand pulp mill

Waste wa ter flow from SCA Forest Products,strand plant

Bleaching

sequence

O Z

Bleaching

sequence

D(EO)D(E )D

Bleaching

sequence

( +D)EHDED

0

20

40

60

80

100

120

140

1980 1982 1994

Year

m3/ton90%drp


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Development of emissions of CODSCA Forest Products, strand pulp mill

COD levels after technical improvementsatSCAForest Products, strand plant

M t b o

tr tm t

zo ,

o d r t,

T F b

IT , Improv d

w ,

N w oxy

b

xy b

ear

k

CO

Dtonpulp


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Development of emissions of AOXSCA Forest Products, strand pulp mill

AOX levels after tec nical improvements at SCA ForesProducts, strand plant

h rC

TC h

TC rh

MC-

h

h

h r

ear

AOX/tonpulp


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Solid wastes

Dirty wood chips or fibers as well as bark.

The broken, low-quality fibres are separated

out to become waste sludge.

All the inks, dyes, coatings, pigments, staples

and "stickies" (tape, plastic films, etc.) washed

off the recycled fibres.


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Organic wastes amount developmentSCA Forest Products, strand pulp millOrg an ic w aste to lan d ill 85- 5, SCA Forest

products, strand mill

0

20

40

60

80

100

120

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

ear

ton

ea


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Cleaner production measuresRaw materials

aintaining moisture content of the rawmaterials constant all year around.

Keeping c emical inventory to a minimum andbuying small containers of infrequently used

materials.

Labelling storage area for hazardoussubstances.

Providing spill containment and collectionsystems during storage.

Genetically modifying forest trees.


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Genetically modified trees

Lignin is the main wood

component that must be

effectively removed from the

pulp.

It has been possible to use

genetic engineering to modify

lignin content and/or

composition in poplars.

courses.washington.edu


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Advantages of genetic modifications

Genetic modifications improved characteristics,

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

quality pulp.

Owing to th

e genetic modification savings inenergy and pollutant chemicals are achieved,

thus leading to an environmentally more

sustainable process.


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Debar ing

Wet Dry

Waste water m3/t 3-20 0-5

SS kg/t 15-50 0-10

BOD5/t 5-10 0-3

Energy consumption

kWh/t

20 20


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Cleaner production measuresWood yard (1)

Pulp mills integrated wit lumbering

facilities: acceptable lumber wood is removedduring debarking; residual or waste wood fromlumber processing is returned to the chipping

process; in-house lumbering rejects can be a

significant source of wood furnish. Avoiding ydraulic debar ing saving

energy and water consumption, reducing

wastewater amount.


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Cleaner production measuresWood yard (2)

Reusing leac ate water.

Co production from bar : mulch, groundcover, charcoal.

Burning bar from debarking and small chipsfrom chipping for energy production (dependson the moisture content).


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Cleaner production measuresPulp production (1)

Increasing brown stoc was ing efficiency.

Any remaining cooking liquor will increase th

echemical consumption in subsequent stages.

Water reuse from evaporators. Theevaporation plant is always one of the largest

steam consumers in the mill. Condensate mightbe used instead of fresh water in the mill.

Repulping t e rejects from screening ratherthan putting them into the landfill.


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Cleaner production measuresPulp production (2)

Using pulp centrifuging to remove anyremaining impurities.

Sludge utilization by means of land-spreading. This method of sludge disposal isan area of concern, as sludge constituents arenot well identified.

Air emissions control devices.

Providing spill containment and collectionsystem.


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Cleaner production measuresChemicals recovery (1)

Using of new technologies (C P, BLG, heat

transfer,h

eat exch

anger). Improvements technical parameters of

recovery boileror furnace (geometrical shapeetc.).

Using light gas strippers and gas collectionsystems which will remove hazardous and foulsmelling pollution from the air and increaseworkplace safety.


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Cleaner production measuresChemicals recovery (2)

Deaerator tan s ahead of the boilers tohelp reduce the intake of freshwater.


Providing spill containment and collectionsystem.


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Cleaner production measuresBleaching

Avoiding chlorine bleaching.

Continuing research on biotechnological

bleaching and electrochemical bleaching.


Providing spill containment and collection

systems.


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Cleaner production measuresPaper production (1)

Cleaning the roll in the paper machines to

avoid broken paper line. Adjustment of edge cutter to reduce side

trimming loss.

U

se of soft water as a boiler feed water. Recycling water evaporated from drying

process by condensing.


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Cleaner production measuresPaper production (2)

Optimizing the thermal effects on water

used in the paper machine and stockpreparation area.

Providing dis save all for paper machine.

Repulping rejected paper in a closed loopmanner.


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Cleaner production measuresProducts processes and recycling

Increasing recycling rates. Recycling

reduces energy consumption, decreasescombustion and landfill emissions, and

decreases the amount of carbon dioxide in

the atmosphere. This process also saves

money.

Possibility for easy pac aging recycling.

Using green fuel for transportation.


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Recycling

In Europe an average of 56% of used paper is

recovered. The recycling process includesfollowing stages:

Sorting

Dissolving

De inking

ixing

Papermaking process


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Ideal paper mill (1)

From cleaner production point of view is a

chlorine-free and zero-discharge one, withminimized quantity and toxicity of air pollutionand solid wastes.

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.


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Ideal paper mill (2)

Such an approach is developed in the form ofpaper recycling, different types of substancesre-use during production processes, co-production and chemicals recovery.

Future research can develop more sustainable

reuse options for kraft pulping solid wastes, aswell as pulping methods that result in purifiedby-products that can serve as feedstock forother manufacturing processes.


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lec 7- pulp and paper industry (f)

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