group7_pulp and paper product

8/2/2019 Group7_pulp and Paper Product

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PULP AND PAPER

GROUP : 7

Vijay Kumar Das 09CH1037

Abinash Dalei 09CH1038

Debashis Roy 09CH1039

Deepak Kiran BS 09CH1040

Ramkrishna Hari Kouraik 09CH1041

2012


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PULP AND PAPER PRODUCT

INTRODUCTION:

Pulp is a fibrous and cellulosic material derived from chemically or mechanically separating

cellulose fibres from bamboo, bagasse, woods or waste papers. In India, the main source of

feed for papermaking industries is bamboo and wood. Generally, Pulp is now obtained from

softwoods (Pine, Larch etc) and Hardwoods (Eucalyptus, Birch etc).

In any Country, the demand for Paper products is a measure of the educational, social,

cultural and industrial activity of it. Paper is used not only as a printing material but also for

packaging, chemical pulp etc .The requisites for any cellulose raw material for pulp and

paper industry are many:1) ample supply of pulp 2)availability 3)Good storage and handling

4)cost of conversion 5)facility high yield of qualityfibres.

Indian paper industries can be classified into six classes as follows:

1. Large integrated paper and paperboard unit using conventional raw materials likebamboo, wood etc with in house pulping facility.

2. Small paper units based on either only on non-conventional raw materials likebagasse, wheat and rice straws or imported pulp.

3. Small paper units based on waste papers.4. Paper units near sugar industries utilizing the bagasse materials produced as the final

waste product.

5. The large integrated newsprint manufacturing units.6. Hand paper production units, using cotton rags, jute wastes, cotton liners etc.Raw materials used in paper industries are:

Softwoods including coniferous and non-coniferous woods. Grasses and reeds including lemon, panni, sarai grass, bamboo etc. Straws like rice, wheat, bagasse, barley, reeds etc. Hardwoods like acccia, lemon, gum, Mysore gum etc, eucalyptus, pines, patula,

paper mulberry and rubber plant wood.

Cotton liners.Demand In India:

The demand of paper products are growing at a steady rate as given:

Year Cultural Industrial Total

1991-1992 10.5 11.5 22.0

1995-1996 13.2 15.4 28.6


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2000-2001 16.8 21.1 37.9

According to sources, demand for raw material in 2010 was total 62.97 lakh tons and

production of raw material was 31.54 lakh tons with a gap of 31.43 lakh tons. Around

2015 this gap is expected to increase about 46.56 lakh tons.

METHODS OF PRODUCTION:

The major processes of paper production are: Sulphate or Kraft process, Thermochemical

process, Semichemical process and Sulphite process. Among these, Kraft process and

Sulphite process are most common.

Kraft Pulping:

Pulp processing:

It is the most popular process today. All types of fibrous raw materials can be used as feed

and chemical reagents used are: 60% NaOH, 25% , 15% in 10-15% aqueous

solution. Although all sorts of woods can be cooked by this method and good, strong fibres

are obtained, chemicals used should be recycled and regenerated along with eliminating

steam pollution. The major steps involved are as follows (for continuous digester):

Logs are debarked by tumbling and rubbing, conveyed to the chippers containinglarge rotating disks with heavy knives to reduce the woods to chips of preselected

sizes (2-5 cm flat chips).

The chips thus produced are screened to separate the oversized chips and thedesired products. The oversized chips are sent back to rechippers to reduce them in

proper size.

The chips are then sent to continuous digester and presteamed at 100 kPa volatilizingturpentine and noncondensable gases. These are then passed to a high pressure

impregnation zone at about 900 kPa, where temp(170C) is adjusted and cookingliquor is produced(cooking time:1.5 hours). A quench flow of cold black liquor stops

the reaction. Some pump around reflux system is also provided.

The Brown stock is withdrawn as side streams and circulated through external heatexchangers to reheat and control the digestion temperature within. These are

adjusted so that maximum lignin removal is accomplished with min cellulose

hydrolysis.

After heat removal this is sent to s strainer to separate into pulp slurry and blackliquor. The pulp slurry is passed through a blow-down valve and sent to a blow tank.

In blow tank, residual heat is recovered in the form of steam which is used for feed

preheating.


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Then the pulp is screened to remove wood knots and undigested residue. Then it isfiltered to remove black liquor which is sent either to recovery or modification

section.

The brown pulp obtained from filtering goes either to product finishing or to thebleaching unit. By bleaching improvement of fiber quality and degree of whiteness is

achieved with minimum degradation action on cellulose.

Bleaching Of Pulp:

Bleaching of the pulp is done in a stepwise fashion. In a batch or continuouschlorinator, liquefied Chlorine is vaporized and added to 5% solid aqueous pulp. The

operation takes approx. 1 hour at room temp. Then the acidic solution is washed on

acid proof thickening rolls and passed to caustic soda digestion to solubilize

converted colour bodies (1-2% caustic solution in 10-12% solids slurry at 60-70C).

In the next step, Calcium hypochlorite is added at pH of 8 for oxidative bleaching. Theresidence time is 2-3 hour at 50C. For some improvement in colour, the pH can be

lowered to 5-6 by treatment with Sulphur dioxide gas.

For higher brightness, Chlorine dioxide at pH 5-6 and at temperature 60-70C is used.Also sodium chlorite in mild alkaline condition can be used. These are used only at

the final stage.

Finally light reflectance with a standard white body like MgO (rated 100%) iscompared and necessary process control is done. The bleached pulp has reflectance

o 80-85%.

Earlier chlorine and its derivatives were used for bleaching thickened pulp but now itsuse has been decreased. Chlorine bleaching has been found to produce dioxins and


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other undesirable components of the bleacher effluent in wastewater. For this

reason, the use of chlorine has steadily been decreased leading to closure of several

chlorine plants.

Chlorine has been replaced to a substantial extent by Hydrogen Peroxide addedtogether with sodium hydroxide, used as the activating agent. As hydrogen peroxide

is a highly unstable compound (dissociate readily), a stabilizer is needed to maintainthe effective concentration of peroxide. Recently Sodium Silicate is the most

commonly used agent which forms a scale or thin crust on the internal heat transfer

surfaces of the pulp mill equipment which must be removed in periodic downtime by

organic agents available.

When the pulp is a captive paper type, the wet pulp is taken to the beater operationsto produce paper.

Black Liquor Recovery:

From the blow tank, black liquor containing 98-99% of the digestion chemicals isobtained which must be recovered to avoid water and air pollution and balanced

economy.

Firstly, the liquor is concentrated in calandria multiple effect (5-6 stages) evaporatorsfollowed by disk evaporators to 15-18% solids, at which point combustion can be

sustained in a smelting waste heat boiler (around 60% solids). Makeup and S

are added in the mix tank and sent to the Thomlinson furnace.

The solution is sprayed directly in the furnace where organic carbon burns to supplyheat and C and produce an inorganic molten slag or smelt.


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The molten slag is allowed to fall into a dissolver to come into contact with coldwater and yield green liquor. This liquor is sent to a clarifier to settle the insoluble

impurities (unburned carbon).Any carbonate is then causticzed by adding slaked lime

in a lime slaker.

The resulting slurry is separated in settlers and rotary continuous filters (Filteringmedium: Monel metal screens).Here Calcium carbonate is separated and sent back toa lime kiln to recover CaO for recycle. The filtrate is the white liquor containing

NaOH, and small amounts of, , and .

The major reactions involved in the Pulping process are:

Digestion section:

R-R + NaOH = ROH + RCOONa.

R-R+ = Mercaptans.

Chemical Recovery of Black Liquor:

Smelting Furnace:

2NaR + air () = + , + 2C = +

Causticizing:

CaO +

Major Engineering Problems:

Choice Of Process: The demand for high strength good quality paper products in theworld market has favoured the Sulfate process than Sulfite process. Unlike Sulfite

process, raw material quality has less significance for Sulfate process, also Sulfate

fibres has higher strength properties. Research is being done to run both processes in

same plant.

Soda Process: In India, small capacity (25-50 tons/day) plants use soda process whichinvolves hydrolysis with NaOH and in 4:1 ratio. It is very cheap if chemicalsare not recovered. Also no S is used. But this is a batch process where which produce

inferior grade pulp at high cost and not economic for modern industries.

Pollution: Pulp and Paper mills use large water, steam, makeup S which cause air andwater pollution. Pulp manufacturers have undertaken major research and

development program for waste disposal and water reuse.

By Product Recovery: Among the by-products form the black liquor recovery plant istall oil (a black, sticky, viscous liquid composed mainly of resin and fatty acids), rosin,

turpentine etc. These products are in steady demand with vigorous product

application research and derivative production (Camphor from turpentine).


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PAPER PRODUCT

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 in manufacturing paper from wood pulp and other fibre

pulp, and may also manufacture converted paper products.

Paper is defined as matted sheets of fibers, usually cellulosic and generally formed on a fine

wire screen from a water suspension.

TYPES OF PAPER PRODUCTS (Based on Requirements and characteristics)

Tissue Paper: Cigarette, toilet, napkins. Writing Paper: Bond Weight, Linen papers. Book Paper: Textbook papers.

RAW MATERIALS

1. Fibrous raw Materials Paper Pulp: Ground wood, Bleached and Unbleached pulp.

Choice depends on end uses and requirements.

Reuse pulp: Paper product such as Newspaper & paperboard arerepulped and mixed with new pulp for paper feedstock.

2. Non-Fibrous Raw Materials Inorganic Raw Materials: Clay, talc, calcium sulfate, alum. Organic Raw Materials: Rosin, glue, waxes, glycerol

METHOD OF PRODUCTIONS

The following steps are involved in paper productions;-

1. Preparation of fibre suspensionsPulps are water slurried by mechanical disintegrators of various designs. Fillers are

added to the slurry to increase the brightness, softness and flexibility of finished

paper. Colouring agents are also added into the slurry before processing.

2. Formation fo paperConversion of fiber suspension to paper involves 3 steps

a. Random Arrangement of fiber into wet webA wet sheet is formed by running 99.5% water fiber slurry on to a endless belt

of wire cloth. Water drains by gravity, a part is next removed by a pressure roll


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and a suction roll. The water collected in these machines is called as white

water and reused to obtain maximum recovery of fiber and to conserve water

and to prevent steam pollution.

b. Removal of free water from wet web by pressing and compactionThe wet paper sheet containg 80% water is fed to press section where water is

removed by mild pressure to reduce the water content to 60-65%.

c. Progressive Removal of addition water by heated rollsWhen the paper leaves the press section, it has a dry content

of up to 60-65%. Now, the remaining water has to be removed

by vaporisation. The most common type of paper drying is

contact drying on cylinders heated with vapourThe sheet from the press

section passed through smoothing section, then a series of steam-heated

metal cylinders where heat and moisture are transferred to a felting belt

running on the top of the paper. As sheet leaves the last drying rolls it has 5-6%water.

Process Flow Diagram of paper Industry

Traetment and Packaging

Its wound on large rolls and transferred to the finishing department where it

may be cut, coated and packaged.


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Press section Drying section Reel Cutter Section

Recent Improvements in Paper making

Modification in paper machines to Improve quality of papersResearch is going on to improve the tensile strength of paper. It incorporated a

rubber belt before the pressing rolls which can be varied in degree of elongation.This leads the fiber on the wet web can be compressed and intertwined to give

improved strength final paper.

Increase in wet-strength of paper productsAddition of resin, plastics such as polyethylene are responsible for the increased use

of product under varying moisture condition.

Environmental Problems

Regulated wastes and emissions from the pulp and paper industry include liquid andsolid wastes, 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.

Wastewater releases include chlorinated phenolics, dioxins, furans and otherchlorinated compounds, phosphates and suspended sediments.

Paper mills also produce non-hazardous solid waste such as sludge derived from

their pulping and bleaching operations.

Simplified Flow Diagram fo a integrated Mill


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Pollutant in Effluents

The most common organic pollutants are suspended solids (SS): lost cellulose fibre, dissolved organic compounds such as dissolved lignin compounds,

carbohydrates, starch and hemi-cellulose

Acidic compounds are predominantly natural resin acids. Chlorinated organics (AOX) are found if elemental chlorine is used in the process.

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.

Production of DMS and DMSO from lignin:

The process flow diagram is presented below:


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As we saw in Kraft process we have separated the cellulose content of wood from

the mixture of lignin and non cellulose content.So our filtrate in the Kraft process i.e. the black liquor contain both lignin andnon-cellulose content and thus this black liquor is a source of 2 useful compoundsDMS and DMSO,which require lignin for their production.

The black liquor is concentrated up to 45-50% solids and along with moltensulphur it is pumped into a reactor that is supplied with steam at 2300c and has anoperating pressure of about 35atm. At this high temperature and atmospheredemethylation talks place from the black liquor and sulphur gets attached to themethyl forming DMS.

Now from the reactor we have vapors of black liquor DMS and methylMercaptans.

Immediately the top product from the reactor is sent to a flash distillation unitwhere the demethylated black liquor is separated as a bottom product

Then we condense the vapors of the top product and send it to a water separatorwhere the water gets separated


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Now we are left with Mercaptans DMS and other products in small quantities

In order to separate the Mercaptans we send it to scrubber with NaOH suppliedfrom the top.

Then the Mercaptans are separated and the resulting top product is dried in a

drier.After this we send the entire mass to a distillation column to separate DMS andother impurities.

Hence we have obtained DMS as a top product of the distillation column

We can either stop the process here or also produce DMSO by oxidizing it withN2O4.

Reactions for production of DMSO

2(CH3)2S + N2O4 ---------------- > (CH3)2SO + 2NO

2NO + O2 ------------------------ > N2O4

The DMS produced is blended with N2O4 and sent to a reactor to give DMSO .Thereactor is also supplied with O2 for the oxidation of NO to N2O4 then the top

product coming out of the reactor contains DMSO and N2O4 and other impuritiesand these are first sent to a neutralizer to neutralize the effect of N2O4 andfollowed by an evaporator to remove the NaOH content that came from theneutralizer section.

Finally the top products are sent to a distillation column where we separate theother impurities and DMSO.

Hence We obtain DMSO as the bottom product.

References

1.Outlines of chemical technology by Charles E. Dryden.2.Encyclopaedia of chemical Technology by kirk and Othmer3.Chemical Process Industry by Shreves.

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