Paper Making Process by Nirjhar

WELCOME IN THE WORLD OF PAPER

Let us have an overall concept of paper making process with Nirjhar Chakravorti

Nirjhar Chakravorti, a Mechanical Engineer by profession, has completed engineering in the year 2000, from Jalpaiguri Government Engineering College, India. As an engineering professional Nirjhar has worked at different industries. Nirjhar’s interest is to know different technology and process engineering. During study about paper technology, Nirjhar has prepared this presentation, which can be helpful for those who wants to know the complete cycle of paper making process.

Paper An essential part of life………… Culturally Economically Socially

Indian paper industry is growing today Paper usage in India is very less, compared to global scenario (less than 5% of total world wide paper usage) In 21st Century India is booming, and so Paper usage is also rising

PULP VIRGIN FIBER WASTE PAPER PAPER RECENT DEVELOPMENT TRADITIONAL De-inking Process

Paper is processed broadly in 3-steps: Stock Preparation Approach Flow System Paper Making Process

Stock Preparation Stock Preparation means…. Preparation of Pulp. Pulp is processed, cleaned and bleached Cellulose Fibers along with water which is present in semi-solid state.

Percentage of solid materials or dry substance (i.e. Cellulose fiber) in the sample of stock is defined as Consistency. Consistency is an important term in Paper Technology.

Other important terms: Moisture Ratio: Ratio of weight of water and weight of dry substance in a sample of stock or paper. Basis Weight: Weight in grams of one square meter after paper has been conditioned in a standardised environment (usually at 20 0 C temperature and 50% relative humidity)

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical

Pulper The waste paper is slushed in a continuously running pulper in medium consistency (10-14%). Pulper is agitator of raw material, chemical and water. Chemicals added in the pulper are: Sodium Hydroxide, Hydrogen Peroxide, Sodium Silicate and Soap.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer

Fiberizer The fiberizer is used for mixing dilution water into the suspension and for removing coarse contaminants. The pressure produced by the fiberizer rotor conveys the contaminants and part of stock suspension to downstream screening unit.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept

Dump Tower Dump Tower is basically a storage tank. In Dump Tower, pulp gets sufficient retention time for chemical reaction, along with the chemicals added. From Pulper to Dump Tower, the production is Batch type.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner

High Density Cleaner The High Density Cleaner cleans stock separation of sorted and unsorted waste paper. Relatively coarser contaminants such as small bolts, stones, wires and knots are separated. Cleaner protects machinery downstream against damage and rapid wear.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen

Hole Screen Pulp is passed through multi-stage screen of Ø 1.2 mm holes. New developed machines, with special rotor geometry and Ø1 mm hole screen, can clean fibrous stock suspensions at consistencies up to 3.5%. In Hole Screening, contaminants removed at the beginning stages of stock preparation.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell

Floatation Cell After Hole Screening, stock goes to Primary Floatation Cell, through Stand Tube. Additives are added in Stand Tube. Purpose of Floatation: To enhance brightness to high degree. To reduce dirt and stickies efficiently Floatation Cell Continues….

Floatation Cell Floatation Machine comprises of cells in series forming a horizontal tube with elliptical cross section. A weir extending over the entire aggregate separates the suspension chamber from the foam collection channel. Suspension is removed uniformly from the bottom of each cell and pumped via aeration element to the next cell. Floatation Cell Continues….

Floatation Cell Function of aeration element is based on step diffuser design. Acceleration in the aeration tube generates a vacuum, which sucks the necessary process air, which forms bubbles in the stock. Bubbles remove particles from the stock suspension. Floatation Cell Continues….

Floatation Cell Dirt laden bubbles rise to the top of the cell, forming a foam layer. The foam layer carried over the wire into the foam collecting channel. The cleaner stock suspension remain in the cell and pumped to the next level.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Reject from foam chamber

Combined Floatation System Two stage floatation system is an important feature of modern de-inking plant. The primary floatation stage ensures high stock purity, while the secondary stage optimises floatation yield without sacrifice of brightness and cleanliness. Floatation foam from the primary stage is further deaerated in a cyclone before pumping to the secondary stage. Floatation Cell Continues….

Combined Floatation System In Secondary Cell, usable fibers are recovered from the foam, and the rejects from the Primary Stage are selectively removed from the system. The accept from the Secondary Stage is returned to the Primary Stage inlet.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Accept Reject CL1 CL2 CL3 CL4 Reject Accept Reject Accept Reject Accept stands for Heavy & Light Weight Cleaner CL

Heavy & Light Weight Cleaner After Floatation, light and heavy weight contaminants are cleaned in multi-stage cleaner. Multi-stage cleaner operates in the concept of cyclone cleaner.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Accept Reject CL1 CL2 CL3 CL4 Reject Accept Reject Accept Reject Accept Slot Screen Accept

Slot Screen After Cleaning, stock passes through the multi-stage Slot Screen Arrangement. Cleaned stock is pumped to the vertical screen. Accept from first stage Slot Screen pumped to the Disc Filter. Slot Screen Continues….

Slot Screen Reject from the first stage Slot Screen pumped to the second stage Slot Screen, via storage tank. From second stage Slot Screen, accept pumped to Disc Filter, and reject pumped to third stage Slot Screen via another storage tank. Slot Screen Continues….

Slot Screen From third stage Slot Screen, the accept goes to the tank placed in between first and second stage Slot Screen and reject goes to the sludge tank.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Accept Reject CL1 CL2 CL3 CL4 Reject Accept Reject Accept Reject Accept Slot Screen Accept Disc Filter

Disc Filter After Slot Screen, pulp is dewatered in the Disc Filter. The recovered water is re-used in various locations. For pulp dewatering, feed consistencies as low as 0.6% are acceptable. Discharge consistencies of 10-15% can be achieved. Disc Filter Continues….

Disc Filter The filter consists of low volume discs mounted on a horizontal shaft with conical flow channel. The filtrate valve at the outlet end of the shaft has a wear plate and bridges for separating the various filtrate zones. The filtrate valve is connected to a barometric drop-leg that generates the required vacuum. Disc Filter Continues….

Disc Filter The dewatered pulp is removed from the discs by jets of water and the filter cloth is continuously washed with an oscillating shower. The shaft with the discs is built into a vat. Each disc has separate inlet flow vane and weir for optimised pulp distribution.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Accept Reject CL1 CL2 CL3 CL4 Reject Accept Reject Accept Reject Accept Slot Screen Accept Disc Filter Screw Press Heater Disperger The process in Screw Press, Heater and Disperger is called Dispersion .

Dispersion Purpose: Shears off ink particles still adhering to the fibers Reduce size of ink and stickies and disperse them in the stock suspension Technological treatment of fiber Transport of stock Mix bleaching additives Dispersion Continues….

Dispersion Function: Dispersion effectiveness depends on two operational parameters: Temperature Shear force ψ Stock temperature up to 100 °C are adequate for dispersion. A reduction in fiber strength, which is expected above 100°C, will not therefore occur. ψ Shear force of a certain integrity must be created during mechanical treatment. Dispersion Continues….

Dispersion Dispersion system generally includes three process stages: Dewatering, achieved by Screw Press Heating, achieved by Heater Dispersion, achieved by Disperger Dispersion Continues….

Dispersion Function of each stage of dispersion: Dewatering: Increase consistency and viscosity for high shear forces, Remove dissolved contaminants Heating: Soften stickies and inks Reduce micro-organism Dispersion: Make stickies and inks floatable Disperge coating grits Mix in bleaching chemicals Dispersion Continues….

Dispersion Type of disperger: Disc Disperger Kneading Disperger Disc Disperger: In Disc Disperger, movement of stock is in radial direction. Kneading Disperger: In Kneading Disperger, movement of stock is in axial direction. Disc Disperger Kneading Disperger Dispersion Continues….

Dispersion Dispersion Continues….

Dispersion Disc Disperger: Stock passed through the clearance between two plates along with projected fills. Shearing of ink particles takes place due to the relative rotational movement of the plates. Kneading Disperger: Shaft with projected fills placed axially in a cylindrical housing. Fills projected in the internal wall of the housing. Shaft rotates and stock moves axially. Shearing of ink particles takes place due to relative motion of the shaft and the housing. Dispersion Continues….

Dispersion Possible influence of the Dispersion on fiber quality: Curl Fibrillation/Flexibilisation Dispersion Continues….

Dispersion Curl Effect of curl on fiber quality: Higher wet strength and shrinkage Higher absorption capacity and porosity Higher bulk and greater softness Lower static strength value Lower dewatering resistance Lower apparent fiber length Dispersion Continues….

Dispersion Curl origin of curl: In principal curl originates during all fiber treatment processes where sufficiently high forces act on fibers which can not escape these forces. Curl originates in the high consistency stock ( >20% consistency), as well as medium consistency stock and paper machine itself. With increasing temperature curl and the porosity in the stock increases and tensile strength decreases. Dispersion Continues….

Dispersion Curl Reversible curl: All the curls generated in stock preparation, do not present when it reaches the paper machine. A certain percentage of curl is always reversible during process, depending on furnish and operating parameters. Dispersion Continues….

Dispersion Curl influence of dispersion machine type on curl : Curl generated in both type of disperger. The porosity increase after Disc Disperger is much less and disappears during hot disintegration. The increase in porosity after Kneading Disperger is clearly measurable. Dispersion Continues….

Dispersion Curl Dispersion Continues….

Dispersion Curl Influence of furnish on curl: Wood containing stocks have a high proportion of reversible curl and wood free stocks are largely irreversible. The curl in wood containing stock behaves like elastic fiber. when these fibers are bent they absorbs distortion forces, and as soon as they get chance (e.g. by dilution or agitation), they straighten again. The curl of wood free kraft paper behaves like plastic fiber. These fibers contain amorphous zones, which are in a state of plastic flow above their softening temperature and can not absorb any stress. Dispersion Continues….

Dispersion Fibrillation/Flexibilisation: while curl leads to loss to strength, some dispersion processes have the effect of enhancing strength. They can therefore be compared with refining. To achieve large increase in strength, the Disperger can be operated cold without prior heating.

Preparation of Pulp from Waste Paper Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Accept Reject CL1 CL2 CL3 CL4 Reject Accept Reject Accept Reject Accept Slot Screen Accept Disc Filter Screw Press Heater Disperger Floatation Water Thickener Reductive Bleaching Storage Tower Mixing Chest China Clay+ soap stone Intermediate Chest Machine Chest

After Dispersion….. After Dispersion, water is added to the stock and the stock again passed through flotation second cell and thickener for further treatment. After reductive bleaching it goes to the Storage Tower. From Storage Tower stock goes to the Machine Chest through Mixing Chest and Intermediate Chest.

Preparation of Pulp from Waste Paper: Complete Cycle Waste Paper Pulper Belt Conveyor Water Chemical Fiberizer Dump Tower Drum Screen Reject Accept High Density Cleaner Hole Screen Stand tube Floatation Primary Cell Venting Cyclone Foam Tank Floatation Secondary Cell Accept Reject CL1 CL2 CL3 CL4 Reject Accept Reject Accept Reject Accept Slot Screen Accept Disc Filter Screw Press Heater Disperger Floatation Water Thickener Reductive Bleaching Storage Tower Mixing Chest China Clay+ Soap Stone Intermediate Chest Machine Chest

Stock Preparation The steps and the equipments described here in the process flow is for general idea. Sometimes steps and equipments vary depending on process requirement, quality of fiber, end product, etc. But as a whole the steps remain same.

Approach Flow System Approach Flow System also known as Wet End Process. Advantages of Approach Flow System: Ж To reduce Stochastic Variations: Perfect homogeneity of the stock in the headbox No uncontrolled fluctuations in the headbox consistency Low signal noise level at the headbox Ж To reduce Periodic Variations: Very low level of pulses created by rotating elements Fast, stable and accurate control loops Ж To satisfy other requirements: Low air content in the system Stable retention and chemical balance

Approach Flow System Stock Preparation Macro & Micro Mix

Macro & Micro Mix Purpose: Complete mixing of all stock components, including broke and stock coming back from save all. (save all means collection tray of extracted and recovered white water from initial stages of paper making machine, and broke means rejected semi-made papers during process of paper making). To eliminate consistency variations. Attenuation of fluctuation.

Macro & Micro Mix Features: Macro mix takes place in the mixing pipe. The feed pipes are tangentially placed to the main pipe. In this pipe, the kinetic energy of the stock is used to provide a high degree of pre mixing. Micro mix takes place in the static mixer.

Approach Flow System Stock Preparation Macro & Micro Mix Jet Mix

Jet Mix Features: Consecutive mixing of components Most intensive mixing at thick stock addition The kinetic energy of backflows is used to premix the streams. Final mixing takes place at the thick stock injection point.

Approach Flow System Stock Preparation Macro & Micro Mix Jet Mix Cleaner

Cleaner In cleaner, dilution water is added in the critical region of the cone, so that fiber losses become less. In smaller systems, three cleaner stages plus an integrated fiber recovery cleaner are needed.

Approach Flow System Stock Preparation Macro & Micro Mix Jet Mix Cleaner Break Tank

Break Tank Purpose: To keep pulsation away from headbox (Head box is the first equipment of Paper Making Machines) Break tank is basically a hydraulic de-coupling between Jet Mix and Head box To deaerate the white water; because air in the system can create problem during paper making, such as amplifying pulsation, pump speed fluctuation and cleanliness related problem

Approach Flow System Stock Preparation Macro & Micro Mix Jet Mix Cleaner Break Tank Slot Screen

Slot Screen Slot Screening machine is important, because it is the last process stage before paper making machine. Purpose of Slot Screen: To efficiently remove residual impurities Policing of fibers Important feature of Slot Screen : No pulsation should occur No stringing should generate

Approach Flow System Stock Preparation Macro & Micro Mix Jet Mix Cleaner Break Tank Slot Screen Pulsation Damping Tank

After Approach Flow System.... Slot Screen is the last equipment of Approach Flow System. After Slot Screen, Stock goes to Pulsation Damping Tank (PD Tank). Name implies that, PD Tank dampen the pulsation to increase the quality of paper. After PD Tank, stock goes to Headbox, the first equipment of paper making machine. The combination of equipments in the Approach Flow System varies, depending on requirements.

Paper Making Machine Enroute to the Headbox, the stock (i.e. pulp) is diluted to about or below 1% consistency. From the Headbox, the stock is distributed in a thin layer onto a endless running fabric, dewatered, pressed and dried to paper of a dryness of about 95%.

Paper Making Process Headbox Approach Flow System Pulp Wire Section Press Section Dryer Section Calender Section Pope Reel Section

Headbox The Headbox is an equipment which discharges an uniform jet of paper making stock onto the moving forming fabric. The functions of Headbox are : Spread stock evenly across the width of the machine. Level out cross currents and consistency variations. Level out machine direction velocity gradients. Create controlled turbulence to eliminate fiber floccing. Discharge evenly from the slice opening; impinge on the forming fabric at the correct location and angle.

Wire Section In Wire section, paper is formed on an end-less fabric wire running in a loop across foils and various dewatering element. This concept is called Fourdrinier System. For dewatering from both the side of the paper web and minimum two sidedness of the product, a equipment called Duo Former is used.

Wire Section Major influencing factor for fiber formation: Fiber type and preparation Filler content Consistency Type and arrangement of dewatering element Wire shaking Dandy roll Top wire unit (Duo former) Wire Section has the maximum potential for formation improvement

Wire Section The strength of fiber network being dewatered on the forming fabric (i.e. wire) depends on surface tension and mechanical friction between the fibers. The forces created by the surface tension increase in inverse proportion to the distance between adjoining surfaces, which means wet strength of the paper web increases with dryness.

Press Section After Wire Section, paper web is pressed by multiple rollers in the Press Section. To ensuring good machine efficiency and pressing, a compact bi-nip press followed by a straight press is used. In the Press Section, paper web is conveyed by the felt; drive to the rolls also transmit through these felts.

Press Section Feature: Minimum two sidedness as both sides of the sheet comes in contact with hard rolls Better sheet release and easy paper transfer Minimum open draw Better smoothness and hence, better printability Faster and easier felt change

Press Section In the press nips water is removed by three effects: One part is thrown out of the nip and collected in the pans and channels. Another part is removed by the suction roll Majority of the water is transported by the press felt. So after the nip, the press felt is contaminated with waste water. This felt is cleaned and water is taken out during one revolution to get the felt ready to pass the nip again. For this purpose suction tubes in each felt circuit is used.

Press Section During pressing a new phenomenon comes into play at about 40% dryness, known as Hydrogen Bond. Fiber surfaces are pressed close enough together that the oxygen atoms of hydroxil groups protruding from adjoining surfaces come within a distance of 2.5-3.5 Å to one another. In this situation two oxygen can share a proton of a hydrogen atom. In effect, the hydrogen atom can not choose between the two oxygen atoms, thus producing a hydrogen bond.

Press Section The phenomenon of hydrogen bonding occurs because of the singular geometry of the glucose unit in a cellulose chain. The strength of the hydrogen bond depends on the number of bond per contact surface and on the size of this surface.

Press Section Fiber Structure of Paper & Hydrogen Bond

Dryer Section After Press Section, paper web passes through number of drying cylinders. The cylinders are driven by fabric wires. The classical drying section consists of two tiers of drying cylinders. The cylinders are cast in normal grey iron and coded for a steam pressure of 250-750 kPa depending on the type of paper being made. They are turned inside and outside.

Dryer Section The cylinders are divided into steam groups (usually four), where all the dryers within a group operate at the same steam pressure. The cylinders also divided into drive groups, each group having one directly driven cylinder; the other cylinders in each group are driven by gears or pulled by a dryer fabric. In modern issue machine drying is carried out on a yankee cylinder. Yankee is a cast cylinder having a diameter of 4 to 6 m and coded for a steam pressure of about 1MPa.

Dryer Section The Steam is supplied to and the condensate is removed from the each cylinder. The steam is introduced through a central pipe in the back-side journals. Condensate is entrained by steam through a syphon going to a pipe concentric to the steam pipe. On wide machines syphons may be used at both sides of the cylinders.

Dryer Section In Dryer Section, also hydrogen bonding takes place. As water is evaporated from the wall, annular cracks in the wall makes the wall thinner and stiffer. If the fiber are soft enough, surface tension during drying collapses the lumen and changes the tubular fibers into bonds. These processes are not always desirable and depends largely on temperature. The changes can partly be reversed by refining.

Calender Section After Drying Section, paper is pressed in the Calender section, by calender rolls. Concept of pressing in the Calender Section, is different than pressing of paper webs in the Press Section. Pressing in the Calender Section provides ironing effect in the paper. The calender rolls may be heated or unheated depending on design.

Calender Section Influencing parameters of calendering: Number of nips Compressive stress Temperature or roll in the nip Dwell time of the paper web in the nip Hardness of soft covers Surface properties of the rolls

Calender Section Advantages of heated rolls over unheated rolls: Better paper smoothness achieved at lower line loads Less loss in the bulk for a required smoothness. Less line load required for given paper finish Less damage to the paper fibers Heat reduces the porosity of the sheet surface Improved printability Less temperature variations across the sheet More uniform surface finish

Calender Section Advantages of soft calendering 2x2 rolls: Minimisation of two sidedness of paper Wide load and temperature range Quality range from very rough to very smooth

Pope Reel Section After Calender Section, paper winding takes place in the Pope Reel Section. Pope reel shell is made of cast iron. Primary arms swivel empty reel spool over pope reel into threading position for reel spool changes and then into transfer position on reel spool track. Secondary arms presses spool against pope reel with controlled linear force and pushes the full reel spool into final position. Full reel spool brakes in end position by means of levers and hydraulic shock absorbers.

Doctor One important part of paper making machine is Doctor. Doctor is basically a cleaner…. which cleans the different rolls. For different rolls, doctors of different construction and material are used. apart from doctors, other cleaning arrangements are also used at different sections of paper machines.

Paper Making Machine Apart from these equipments, some optional equipments are used, as per requirement: Size Press/ Speed Sizer Coater After Dryer Section After reeling in the Pope Reel Section, the paper is again re-wound and cut to suit customer’s requirements.

Paper Today different quality of papers are used in the market, e.g.: * Graphic Paper: Newsprint Super calendared Light Weight Coated Wood Free Coated Wood Free Uncoated * Board & Packaging: Kraft Liner Corrugated Medium Folding Box Board, e.g. Cosmetic Pack Liquid Packaging, e.g. milk cartoons White Lined Chip Board Sack Kraft * Special Paper: Cigarette Paper Thermal Paper Photo Base Paper Décor Paper

Paper Today customer is very much quality conscious. So paper manufacturers and paper machine designers are continuously developing new technologies to satisfy customer’s requirement and to meet changing global priorities.

Paper Paper represents the quality of human living and also, human civilisation…. So Quality of paper and also Quality of paper making process is very important…… That’s why paper technology is evolving continually…. and journey through the world of paper technology is a wonderful experience.

THANK YOU Please send your suggestion at [email_address] or [email_address]

Paper Making Process by Nirjhar

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