Pulp production

 Introduction
 Pulp Production
 Properties
 Uses
 Gernalize process of pulp making
 Best process for making pulp
 Environment impact
 Material of construction
 Waste paper pulping
 Advances in pulping process
 References
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Pulp is a cellulosic fibrous material prepared by chemically or
mechanically separating cellulose fibres from wood, fiber crops, waste
paper, or rags.
 Many kinds of pulp are made from wood with nothing else mixed into
them.
This includes newspapers, magazines and even toilet paper.
Pulp is one of the most abundant raw materials.
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Pulp Pulp is a commercial fibrous material obtained from bamboo,
wood, bagass (waste material) etc. by mechanical and chemical
means.
Paper mill primarily are engaged in manufacturing paper from
wood pulp and other fibre pulp, and may also manufacture converted
paper products.
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spruce,
pine,
fir,
larch
and hemlock
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 Dirt content of pulp particularly of recycled pulp is important for
its suitability to make fine paper.
 Moisture Content of Market Pulp is important from storage,
transportation and handling point of view.
 Fiber Length of Pulp is one of the most important parameters of
pulp.
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1. Raw material Process:
 Wood is the main fibrous raw material used to produce pulp, and
accounts for more than 90% of the production.
 Preparation of the raw material is necessary before it enters the
papermaking process.
 Wood, for instance, first needs to be debarked usually by
mechanical or hydraulic processes, and is then disintegrated,
generally by chipping into particles of the adequate size.
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The goal of pulping is to separate the fibres from the
material
There are 3 different groups of pulping methods are:
1.Mechanical pulping
2.Chemical pulping
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 This method consists in grinding raw material against an abrasive
surface to defibre the raw material (more generally softwood)
without any lignin dissolution.
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 This method separates the fibres from the raw material by making
soluble all the non-cellulosic components in a cooking liquor at high
temperature and pressure. This pulping gives better quality but
greater pollution.
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 Pulp for packaging material can generally be used without bleaching.
For other purposes, it has to be bleached.
 In mechanical pulping most common agents are sodium or hydrogen
peroxide and sodium hydro sulphite used alone or in combination.
 In chemical pulping chlorine, sodium or calcium hypochlorite and
chlorine dioxide are used.
 Oxygen pre-bleaching becomes more important in order to reduce
chlorine use.
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1. Kraft process
2. Sulphite process
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The production process can be divided into 8 sub-processes:
Debarking & chipper bin
Impregnation
Cooking
Recovery process
Blowing
Screening
Washing
Bleaching
Process chemicals 2219-04-2020

 Debarking is the process of removing bark from wood. Debarking generally
involves the use of industrial machinery into which the log or stake is placed.
Generally they are powered by hydraulic motors.
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Chipper bin:-
Chips are fed in this device.
Cut logs are conveyed to the chipper where rotary disks
with heavy knives reduce the wood to size 2-5cm flat
chips.
 Size reduction is done to maximize penetration of
process chemicals.
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IMPREGNATION
• Common wood chips used are 12–25 millimeters long
• Prestreamed and wetted to impregnate the chips with white liquor
• White liqour contain NaOH + NaSH
 COOKING
• enters the digester below 100 °C (212 °F).
• Typically delignification requires several hours at 170 to 176 °C
(338 to 349F).
• The combined liquids, known as black liquor contain lignin fragment
from the breakdown of hemicellulose, sodium carbonate, sodium
sulfate and other inorganic salts
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BLOWING: cooked wood chips are blown by reducing the
pressure to atmospheric by release of steam. Reduces the
pressure of steam from 80 to 10 atm .
SCREENING: Screening of the pulp after pulping is a process
whereby the pulp Is separated from large shive, knots, dirts
and other materials.
 WASHING :
• Pressure diffusers
• Atmospheric diffusers
• Vacuum drum washers
• Drum displacers
• Wash pressure
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In bleaching tower the pulp are bleached to a high brightness
bleaching tower.
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LIGNIN
CONTENT
DECREASES.
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The black liquor (lignin-rich) produced from the Sulfate pulp
production contains 95-98% of digested chemicals. To reduce air
and water pollution and to balance economy of operation, these
chemicals should be removed before disposal.
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 It is a series of single effect
evaporators.
 Multi-effect evaporator and
disc evaporator concentrate
the black liquor from 15-18%
solid to 60-65% solid.
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It is designed with two
agitators to mix the product.
 Make up chemicals (Na2SO4 +
S) are added.
The combustion is carried out
such that sodium sulphate is
reduced to sodium sulphide.
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BOILER
 It produces molten slag.
 Here organic carbon present in black liquor is burned.
 High pressure 28 atm to 30atm steam is produced.
DISSLOVING TANK
 The molten chemical smelt dissolve immediately with cold water and yield
green liquor (aqueous Na2CO3).
Clarifier
 It is used for filtering. It separates calcium carbonate sludge and white
liquor.
 Filtering medium is monel metal.
 Causticizing tank
 It precipitates lime mud.
 Carbonate is causticized by adding Ca(OH)2 4019-04-2020

 The sulphite process is an industrial process to produce wood pulp suitable
for wood low in resin and silicic acid. The advantages of this process are
above all the very efficient delignification, the good bleachability, the high
reactivity during further processing and low investment costs.
 In the sulphite process, the wood fibres are digested in an acidic or neutral
medium. In the process, the lignin is subjected to sulphonation and is thereby
converted into a water-soluble salt which can be removed from the cellulose.
 The by-product lignosulphonates are either commercially recovered or
incinerated (recovery). In case of recovery the black liquor separated from
the fibres during pulp washing is evaporated and burned in the recovery
boiler using oxygen.
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 The very light pulps produced in this way are today used almost exclusively for the
production of chemical cellulose or paper. To produce one tonne of pulp you need
about five cubic metres of wood and 90 kilograms of Sulphur.
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 Stainless steels and other nickel-containing alloys are used
extensively in the pulp industry, providing excellent corrosion
resistance against the process liquors and offering valuable
mechanical properties.
Digesters:
 Previously digesters were constructed from A516-grade 70
carbon steel and austenitic stainless steel.
 Now a days duplex stainless steel is used in digesters.
 Duplex stainless steel is a metal that
combines ferritic and austenitic stainless steel grades.
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High Corrosion resistance.
It does not succumb easily to stress,
cracks, pitting, or abrasion.
High strength.
Design flexibility.
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 Other equipment in pulp industries are mostly constructed from
316L and 304L stainless steel.
304L stainless steel
duplex stainless steel
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Recycled paper (Waste), newsprint and magazine is
charged in Hydraulic Pulper with adding water and
it is being processed till waste paper is converted
into slurry form with high consistency pulp.
Then it is transferred to machine chest where
addition of dye, chemical takes place. This pulp
then is fed to the machine chest.
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Deinking is a recycling technique that can produce high
quality recycled pulp from recovered papers.
Flotation Deinking which makes ink particles hydrophobic
by means of a collector in a flotation cell. The air bubbles
generated at the bottom of the cell carry the ink
particles to the surface where they are confined in foam
which is removed.
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 Chlorine Dioxide
1. Chlorine dioxide (ClO2) is a highly reactive greenish-yellow gas.
2. It is toxic and corrosive, explodes at high concentrations (10%) and is quickly
reduced to Cl2 and O2 in the presence of ultraviolet light.
3. It must be prepared as a dilute gas and stored as a dilute liquid, making bulk
transport impossible.
4. ClO2 is generated by reducing sodium chlorate (Na2ClO3) with either SO2,
methanol, salt or hydrochloric acid.
5. The gas leaving the reactor is condensed and stored as a 10% liquid solution.
Modern ClO2generators operate at 95% efficiency or greater, and the small
amount of Cl2 that is produced will be collected or scrubbed out of the vent
gas.
6. Side reactions may occur depending on the purity of the feed chemicals, the
temperature and other process variables. By-products are returned to the
process and spent chemicals are neutralized and sewered.
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 Sodium Hypochlorite
1. Sodium hypochlorite (NaOCl) is produced by combining Cl2 with a dilute solution
of NaOH.
2. It is a simple, automated process that requires almost no intervention. The
process is controlled by maintaining the caustic concentration such that the
residual Cl2 in the process vessel is minimized.
 Chlorine and Caustic
1. Chlorine (Cl2), used as a bleaching agent , is a highly reactive, toxic, green-
coloured gas which becomes corrosive when moisture is present.
2. Chlorine is usually manufactured by the electrolysis of brine (NaCl) into Cl2 and
NaOH at regional installations, and transported to the customer as a pure
liquid.
3. Three methods are used to produce Cl2 on an industrial scale: the mercury cell,
the diaphragm cell, and the most recent development, the membrane cell. Cl2 is
always produced at the anode.
4. It is then cooled, purified, dried, liquefied and transported to the mill. At
large or remote pulp mills, local facilities may be constructed, and the Cl2 can
be transported as a gas.
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5. The quality of NaOH depends on which of the three processes is used. In the
older mercury cell method, the sodium and mercury combine to form an amalgam
that is decomposed with water. The resulting NaOH is nearly pure.
6. One of the shortcomings of this process is that mercury contaminates the
workplace and has resulted in serious environmental problems. The NaOH produced
from the diaphragm cell is removed with the spent brine and concentrated to allow
the salt to crystallize and separate.
7. Asbestos is used as the diaphragm. The purest NaOH is produced in membrane
cells. A semi-permeable resin-based membrane allows sodium ions to pass through
without the brine or chlorine ions, and combine with water added to the cathode
chamber to form pure NaOH. Hydrogen gas is a by-product of each process. It is
usually treated and used either in other processes or as fuel.
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Reaction Tower:
In bleaching “’Tower” is needed to achieve retention time around 1-4
hours • Critical temperature and chemical environment
• ClO2 is harmful so that use of ceramic tiles on steel or titanium
Chemical Mixer:
• Good mixing itself is a bigger task in a bleaching though there is
progress
• Invention of Medium consistency of about 10%
• Almost Solid pulp becomes a fluidized like water
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Washers:
 In bleaching series, removal of solubilized lignin after every stage. Important
when there is a pH change
 Washing equipment: Drum filters or diffuser washer
 MOC: Highly alloyed SS or titanium due to corrosivity
Pumps:
Transportation of pulp, chemicals, water and wash liquor
• Liquid (4-5% consistency) - Centrifugal pump
• Pulp (10-12% consistency) - MC pump to use fluidization and centrifugal forces
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 Use of soda Process.
 Pollution and waste disposal.
 Recovery of cooking chemicals.
 By product utilization.
 Scale formation in the pulp milling equipment.
 Modified process for other raw materials.
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 Over 20% of The world paper now comes from the
repulping of recycled paper.
There are a great grades produced varying widely in
quality. For such purposes batch process is used.
 Secondary fiber worth about 5 times as its value as
waste paper.
 The largest single use is in the manufacture of multi-ply
cylinder board.
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 Chlorine Free Bleaching: Chlorine bleaching creates a by-product called
dioxin which has extremely harmful effect on the environment. TCF process is
the latest process which uses the oxygen from H2O2.
 Organosolv pulping: This method was developed to reduce the sulfur
emission. The method breaks up lignocellulosic biomass to obtain cellulosic fibers
for pulp and paper making. Organosolv pulping process produce high yield pulp, low
residual lignin content, high brightness and good strength.
 Pulping of Non -Wood Plant Species: This is mostly made up of 44%
straw, 18% bagasse, 14% reeds, 13% bamboo and 11% others.
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Pulping often releases a range of pollutants, including
organic products which cause eutrophication in water,
aluminum salts and sometimes also generation of sulphur
dioxide.
When bleaching is carried out with chlorine or hypochlorite,
it may generate dioxin. These pollutants have direct impacts
on freshwater and marine ecosystems near pulp mills.
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 Air pollution mainly occurs from digesters blow tanks, steam
boilers, chemical recovery boilers.
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 Solid waste is generated in the form of sludge, ash, wood waste,
screening, sand and grit.
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 [1] N. DeKing, Ed., Pulp & Paper Global Fact & Price Book 2003–2004. Boston:
Paperloop, Inc., 2004.
 [2] G.A. Smook, Handbook for Pulp and Paper Technologists, 2nd ed. Vancouver,
BC, Canada: Angus Wilde, 1992.
 [3] F. Kayihan, “A review of modeling and control in pulp and paper industries,”
in Proc. 5th Int. Conf. Chemical Process Control (CPC V): AIChE Symp.
Ser., 1997, pp. 117–132.
 [4] J. Minor, “Pulp,” in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd
ed. , M. Grayson, Ed. New York: Wiley, 1982, vol. 19, pp. 379–419.
 http://en.wikipedia.org/wiki/Pulp_and_paper_industry.
 https://business.mapsofindia.com/paper-and-pulp-industry/
 https://www.stainless-structurals.com/blog/stainless-steel-pulp-and-paper-industry/
 https://www.nickelinstitute.org/about-nickel/pulp-paper/
 http://www.ilocis.org/documents/chpt72e.html
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