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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.
Air emissions control devices.
Providing spill containment and collectionsystem.
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Cleaner production measuresBleaching
Avoiding chlorine bleaching.
Continuing research on biotechnological
bleaching and electrochemical bleaching.
Air emissions control devices.
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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