Recovered Fiber Pulping Note

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    Recovered Fiber Pulping :

    In stock preparation using recovered fibers, used fibers are pulped, purified and

    optionally de-inked. Depending on the paper grade and the type of furnish used, a

    wide variety of recovered paper processing systems can be applied combiningsimilar processes differently to fullfil specific tasks. Generally, these can be in two

    main categories:

    processes with exclusively mechanical cleaning, i.e. without deinking comprising

    products like Testliner, corrugating medium, uncoated board and carton board;

    processes with mechanical cleaning and deinking comprising products like

    newsprint, tissue, printing and copy paper, magazine papers, coated board and

    carton board.

    In a typical processing system, recovered paper is put into a pulper together with hotwater or white water (water from paper machine) and pulped with mechanical and

    hydraulic agitation resulting in disintegration into fibres. For processes with

    deinking, chemicals such as surfactants and NaOH can sometimes be added as

    pulping additives. Low consistency (4-6% dry solids), high consistency (15-20% dry

    solids) and drum pulpers are the three main types of pulpers and there are batch and

    continuous types. Contaminants and clusters are removed by mechanical means

    during pulping.

    For further removal of mechanical impurities hydrocyclones and screens are used.

    Depending on the furnish quality to be achieved, recovered paper processing also

    includes fractionators, dispergers or refiners.A fractionator separates the pulp into

    two fractions rendering it possible to treat short and long fibres of the pulp slurry in

    different manners. The energy demanding process of disperging can be performed

    in order to achieve improved fibre-to-fibre bonding (better strength characteristics)

    in the paper produced and to reduce visible dirty specks in size. A stock preparation

    plant for the processing of recovered paper can be optionally equipped with refiners

    to improve optical and strength characteristics of the paper. Refining is associated

    with a substantial energy demand. An example arrangement for a stock preparation

    plant for processing recovered paper for two-ply Testliner is shown in the figurebelow (BREF, 2010. pp.474-475).

    Although the actual energy demand varies depending on the extent and types of

    contamination and final pulp yields, pulp production from recovered and secondary

    materials is usually less energy intensive. Examples of typical energy consumption

    levels taken for real cases for stock preparation of different paper grades is given in

    table below (BREF, 2010. p. 486).

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    Energy consumption levels for stock preparation of different paper grades (BREF,

    2010. p. 486)

    Packaging

    Paper

    Newsprint Low weight

    coated/Supercalendered

    Tissue paper and

    market pulp

    Recovered

    paper quality

    Sorted mixed

    paper and

    boards,

    recovered

    paper from

    stores

    Deinkable

    recovered paper

    (old newsprint and

    old magazines)

    Deinkable

    recovered paper

    (old newsprint

    and old

    magazines)

    Deinkable

    recovered paper

    (old newsprint +

    magazines); wood-

    free office

    recovered paper

    Electricity

    consumption

    (kWh/t)

    150 -250 300 420 400 500 400 500

    Thermal

    energy

    consumption

    (MJ/t)

    0 (heating may

    be required if

    dispersing is

    applied)

    450 900

    (= 0.2-0.4 tsteam/t)

    650 1100

    (= 0.3-0.5

    tsteam/t)

    650 1100

    (= 0.3-0.5 tsteam/t)

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    Recovered fiber Pulping Schematic :

    Figure 1. Flowsheet of an example stock preparation plant for processing paper for

    recycling for case-making material (two-ply Testliner), BREF 2013

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    Recovered fiber Technologies and measures :

    Technology or

    Measure

    Energy Savings Potential CO2 Emission

    Reduction

    Potential Basedon Literature

    Costs Development

    Status

    Increased Use

    of Recycled

    Pulp

    Use of recovered pulp can

    reduce energy

    consumption by 10 to 13

    GJ/t-pulp (IEA, 2012. p.35))

    .The production of one

    ton of recycled pulp is

    estimated, on average, to

    consume 6.3 to 11.6 GJ

    less energy compared to

    chemical pulp and 6.3 to

    10.6 GJ/t less as compared

    to mechanical pulp.

    (Kramer et al., 2009. p. 27)

    Studies estimate

    the construction costs

    of recycled pulp

    processing capacity at

    around $485/ton of

    pulp. Depending on the

    price of waste paper

    versus virgin pulp this

    may result in up to

    $73.9 per ton of pulp in

    operations and

    maintenance cost

    savings (Kramer et

    al.2009. p. 97).

    Commercial

    Using Drum

    Pulpers

    A study suggests that if a

    vat type pulper is replacedwith a continuous drum

    pulper in de-inking

    operations, energy

    consumption reduction by

    over 25% can be achieved.

    (Kramer et al.2009. p. 97)

    Energy consumption can

    be reduced by 10 kWh/t-

    pulp as compared to a

    batch pulper (NCASI,2001. p131)

    For a 300 t/d

    capacity plant,CO2reductions

    due to reduced

    power demand

    are estimated to

    be 1055 t CO2/y.

    (NCASI, 2001.

    p.131)

    Costs of a continuous

    drum or dry pulper willbe higher than those of

    batch equipment with

    equivalent capacity.

    For a 300 t/d capacity

    plant , annual savings

    are estimated to be

    around $37 000 [2001

    dollars] (NCASI, 2001.

    p.131)

    Commercial

    Fractionation

    of Recycled

    Fiber

    11 to 13% reductions in

    electricity consumption,

    and up to 40% reduction in

    thermal energy can be

    achieved.

    Capital reduction of 13

    to 22% can be achieved

    compared to traditional

    de-inked pulp (DIP)

    lines.

    Commercial

    Upgrading ofStock The option one results inenergy consumption in the The investment andoperational costs of Commercial

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    Technology or

    Measure

    Energy Savings Potential CO2 Emission

    Reduction

    Potential Based

    on Literature

    Costs Development

    Status

    Preparations

    Plants with

    Decreased

    Electricity

    Consumption

    and Emissions

    range 45 kWh/tonne and

    95 kWh/tonne. The second

    option consumes between

    75 kWh/tonne and 175

    kWh/tonne.

    option two are higher

    than that of option one.

    Secondary

    Separation

    Pulper forPulping

    Process in

    Wastepaper

    Treatment

    For a mill with original

    production capacity of 365

    tpd, installation of thistechnology helped

    increase capacity to 445

    tpd and reduced energy

    consumption by around

    146 800 kWh/year (NEDO,

    2008. p.160).

    Equipment cost is

    estimated as 90

    million. Constructioncost is around 30

    million approximately

    (NEDO, 2008. p.160).

    Commercial

    Continuous

    Batch Fibre

    Recovery

    System to

    Processing

    Recovered

    Paper in a

    Complete

    System

    Process is more energy

    efficient.

    Investment costs are

    low.

    Commercial

    Heat Recovery

    from De-

    inking Effluent

    For a mill in the US

    having effluent streams at

    49 C and flow rate of 2.7m3/min, the installation of

    a heat exchanger to

    recover heat and generate

    warm filtered shower for

    the mill's paper machines

    is estimated to reduce

    boiler fuel consumption by

    39 000 GJ/y.

    Fuels savings for the

    boiler are estimated at

    $125,000/y. Capitalcosts had been

    $375,000 with a

    payback period of

    around 3 years.

    Commercial

    Recovery ofBoiler Ash and

    Production of precipitatedcalcium carbonate (PCC)

    CO2emissionsare reduced due

    Production ofprecipitated calcium

    Demonstration

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paration-pulper-pulping-process-wastepaper-treatmenthttp://ietd.iipnetwork.org/content/secondary-separation-pulper-pulping-process-wastepaper-treatmenthttp://ietd.iipnetwork.org/content/secondary-separation-pulper-pulping-process-wastepaper-treatmenthttp://ietd.iipnetwork.org/content/upgrading-stock-preparations-plants-decreased-electricity-consumption-and-emissionshttp://ietd.iipnetwork.org/content/upgrading-stock-preparations-plants-decreased-electricity-consumption-and-emissionshttp://ietd.iipnetwork.org/content/upgrading-stock-preparations-plants-decreased-electricity-consumption-and-emissionshttp://ietd.iipnetwork.org/content/upgrading-stock-preparations-plants-decreased-electricity-consumption-and-emissionshttp://ietd.iipnetwork.org/content/upgrading-stock-preparations-plants-decreased-electricity-consumption-and-emissionshttp://ietd.iipnetwork.org/content/upgrading-stock-preparations-plants-decreased-electricity-consumption-and-emissions
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    Technology or

    Measure

    Energy Savings Potential CO2 Emission

    Reduction

    Potential Based

    on Literature

    Costs Development

    Status

    CO2 Gas to

    Produce

    Recycled

    Mineral Fibres

    for Use in

    Paper

    using boiler ash requires

    up to 50% less fossil fuels

    compared to producing

    CaO from limestone

    quarry (CaCO3).

    to reduced fossil

    fuel use for CaO

    and due to CO2

    being captured

    from

    incineration of

    de-inking

    residues.

    carbonate (PCC) from

    deinking ash as a raw

    material is appealing in

    countries where landfill

    costs are high as it

    gives both economic

    and environmental

    benefits.

    XTREMECleaner

    This technique reduces theenegy consumption by

    50% of as compared to the

    conventional dispersion

    systems.

    The technology savesbetween $3,500 -

    $11,000 per day by

    using low-grade

    furnish.

    Commercial

    Electrohydraul

    ic

    Contaminant

    Removal

    Improved sticky removal,

    floatation and clarification

    may lead to direct energy

    consumption reductions of

    10 to 15% in contaminantremoval and cleaning

    equipment (Kramer et al.,

    2009. p. 111).

    Demonstratio

    n

    Screenable,

    Pressure-

    Sensitive

    Adhesives for

    EnviroSensitiv

    e Labels

    N/A The technology

    indirectly saves

    CO2 emissions

    by increasing

    the recycling of

    wider varietiesof paper.

    Commercial

    Incineration of

    Residues

    One ton of rejects (from

    mills without de-inking)

    with about 45% water

    content can substitute 0.7

    tons of brown coal in the

    boiler. in a German plant

    with 370 000 t/year

    production capacity,

    incineration of rejects in a

    Because the

    rejects help

    substitute coal,

    and about 50%

    of solid matter

    in the rejects are

    CO2natural

    substances, CO2

    emissions are

    The investment cost for

    a co-incineration plant

    including facilities for

    reject pretreatment,

    drying and the

    gasification chamber

    for a reject volume flow

    rate of maximum 3

    t/hour is estimated to

    Commercial

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    Technology or

    Measure

    Energy Savings Potential CO2 Emission

    Reduction

    Potential Based

    on Literature

    Costs Development

    Status

    hearth combustion (with a

    capacity of 28 000 t/year)

    that is integrated in the

    power plant of the mill,

    fossil fuel usage

    corresponding to 66 000

    MWh was reduced.

    reduced. be around 2.5 million.

    In Europe, these can

    provide annual annual

    savings of 0.6 million,

    assuming costs for

    landfilling of 50/t. An

    additional EUR 0.3

    million/yr can be saved

    through the

    substitution of brown

    coal.

    A.

    Increase use of recycle Pulp :

    Use of recycled fibers can significantly reduce energy consumption in pulp production.

    However, as compared to chemical pulping, this can be at the expense of increased CO 2

    emissions, when fossil fuels are used for recovered pulp (IEA, 2009. 138)). There is

    significant potential to increase recycling rates, particularly in non-OECD countries wherethe rates are between 10 to 50%. Whereas the theoretical limit for waste paper recovery is

    estimated at 80%, the limit is believed to be closer to 60% in practice (IEA, 2012. p. 35)

    Recycled pulp produces sludge that can present a disposal problem. Additionally there are

    limitations to the amount of recycled fiber that can be used for a given product (Kramer et al.

    2009. p. 97).

    B. Drum Pulper :

    Many deinking plants use vat type pulpers, often with batch operation. Batch pulpers havehigher energy demand and lower productivity (NCASI, 2001. p. 130). Drum Pulpers can be

    implemented to mills that produce pulp from recovered paper and paperboard. The more

    gentle mechanical action of the drum pulpers make the contaminants to remain intact while

    the paper is defibrated. Drum pulpers have lower energy requirements than conventional

    mechanical pulpers, can use less water, and reduce fiber shortening. However, when drum

    pulpers are used in brown fiber applications, the rapid wetting of furnish and the incomplete

    removal of bailing wire can reportedly cause problems. (Kramer et al., 2009. p. 97)

    Because baling wire must be removed from the paper prior to it entering the drum pulper,

    bale dewiring and bale breaking equipment may be required in addition to the drum pulper ifit does not already exist at the mill.(NCASI, 2001. p. 130)

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    Figure 2. Drum pulper Schematic

    Drum pulper fact is:Drum pulper facts

    1. Drum pulpers are most commonly used in applications that involve deinking

    stock based on recycled newspapers and magazines. The use for brown grades

    is also increasing.

    2. The key benefits offered by drum pulpers are the extremely efficient removal

    of contaminants, even from highly contaminated furnish, and low energy

    consumption.

    3. Typically, a drum pulper consists of a horizontally positioned, gently inclined

    drum tube. In the first zone of the drum, the raw material is disintegratedthrough slushing. In the second, screening zone, fibers are recovered and

    contaminants separated.

    4. The bulk of the work is performed in the drums slushing zone. Accordingly, the

    operational effi ciency of this zone is crucial to the pulping results and energy

    consumption.

    5. Approximately 45% of the raw materials used by the worlds board and paper

    industry is recycled paper. This illustrates the great importance of the efficient

    recycled-fiber lines and processes to the paper industry.

    There are many type of drum pulper, here are the example :

    1. Fibreflow Drum Pulper from ANDRITZ

    The ANDRITZ FibreFlow drum pulper is used for fiber slushing and

    separation of coarse contaminants for all kinds of recovered paper. High

    production capacity and low power consumption in a single unit make the

    FibreFlow drum pulper the preferred choice for continuous pulping.

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    Figure 3. ANDRITZ fibreflow drum pulper

    Wastepaper furnishes are defiberized by means of continuous turnover (via

    dropping and falling inside the rotating drum). This action gently separates

    fibers from contaminants with minimal fiber loss. The contaminants are

    rejected continuously and automatically. The drum has two sections

    (pulping and screening) wetting, chemical impregnation and defiberizingtake place in the pulping section. Fiber recovery and reject separation take

    place entirely in the screening section.

    Benefits of the FibreFlow drum pulper :

    Best-accepted quality, improved ink detachment, and brightness gain

    (thanks to gentle pulping and efficient removal of coarse contaminant

    with minimum fiber loss)

    Highest availability due to single drum machine design with no internalsthat can create wire build-ups

    Reliable and proven mechanics

    Minimum maintenance and efficient single drive

    Suited for all kinds of recovered paper

    2. Optislush Drum Pulper from Metso

    An intensive project to develop the OptiSlush drum pulper was started in

    2001 after careful evaluation of industry slushing needs. The drum pulper

    benefi ted from Metso-wide synergies. For example, the experience gained

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    from Metso Papers Debarking Drum was utilized indesigning, and the drive

    units were designed by an experienced in-house supplier.

    Later that same year the first drum pulper suitable for laboratory research

    and development purposes was introduced and placed in Metso PapersFiber Technology Center at Anjalankoski, Finland. The pilot drum pulper,

    one of the key pieces of equipment in a recycled fiber line, enables perfect

    sim ulation of a mill scale pulper due to the fact that it has the same drum

    diameter. It has a capacity of 100 t/d and is capable of continuous operating

    trials.

    Figure 4. Optislush Drum Pulper

    Benefits of the OptiSlush drum pulper :

    Optimum pulp quality from most of materials

    High performance, efficiency, yield and availability

    Low operating costs and energy consumption Adjustable pulping intensity and time (patented intensity adjustment

    program)

    Easy cleaning and maintenance

    Environmental friendliness

    Flexibility for different applications and rebuilds

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    Here some information about installation in many paper mill :

    C.

    Fractionation of recycled fiber

    Recycling has been greatly issued over the last several years in the paper industry.

    There is an increasing pressure to recycle paper products to manage our resources

    properly. Additionally, paper recycling in many cases is economically favored. When

    using recycled fibers for tissue making, it was shown that it was possible to save up

    to 55% in fiber cost [1]. However, recycled fiber characteristics such as strength and

    flexibility are significantly lower than virgin fiber resulting in poorer quality products.

    Because many physical properties of products are gained through the fiberselection, there is a direct conflict between some physical properties and recycled

    content. Especially in the tissue industry, consumers expect premium quality, i.e.

    high softness and absorbency at a low cost. Therefore, in order to meet the cost and

    quality requirements of the consumers, both recycled and virgin fibers will have a

    place in the tissue industry.

    Fiber fractionation is a term used for a process that splits a feed stream into two

    streams with different properties. The benefit of fractionation is the capability to

    select fibers depending on the product specifications. The two fractionated fiber

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    streams may be treated differently (i.e. refining, chemical addition) and re-mixed

    before being sent to papermaking. A number of advantages may be gained by

    fractionation such as greater strength development of the long fiber fraction,

    enhancement of surface and optical properties with short fiber fraction and

    substantial energy savings due to reducing refining throughput. Kohrs [2] reported

    that the reduction in the investment costs for dispersing and refining in some

    fractionation systems was about one third.

    Musselmann [3] rated several types of equipment for fiber fractionation such as

    thickener, side hill screen, vibration screen, pressure screen, hydrocyclone and

    centrifuge. In addition, flotation cells [4-5] and disc-filters [6] can be used for fiber

    fractionation. To select suitable devices for fractionation, the objective of the

    fractionation and the existing mill conditions must first be considered. Theparameters to be considered when selecting a fiber fractionation system are energy

    cost, throughput and fiber selectivity. Thickeners, side hill screens and centrifuges

    have a low selectivity.

    Repeated recycling causes fibers to become less suitable for papermaking. The

    fibers become less flexible and shorter than virgin fiber and do not conform as well.

    The results of this loss in flexibility and conformability are lower strength and less

    bonding between the fibers,which result in a weaker, lower grade of paper.

    The goals of the fractionation determine the method used. Following fractionation,

    the longer and stronger fibers can be refined to a higher strength, which reduces the

    need for more expensive virgin fiber furnish. Fractionation also results in the

    removal of fines from the furnish by separating out much of this material with the

    short fiber furnish. By separating out short, low-freeness fiber, only the longer

    portion of the furnish needs to be refined, resulting in a possible overall decrease in

    refining energy.

    Fractionation is an integral part of producing multilayer paperboard and corrugatedcontainers from secondary fiber. New cleaning and pulping technologies make the

    production of multilayer paperboard from secondary fiber inviting (1). In multilayer

    paperboard manufacture, fractionation is used to produce a sheet that can be

    altered to fit the required properties (2). The short fraction can be used as the filler in

    the center of the sheet, while the long fraction can be used as liner stock.

    Adjustments may be made to the proportion of long and short fractions to obtain

    desired properties.

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    Similarly, in corrugated containers, The short fraction is used as the corrugated

    medium, while the stronger long fraction is used for the liner (1). The fiber

    separation creates two fiber streams that are more valuable than the feed stream

    alone.

    The greatest problems with utilizing secondary fiber are a continually changing

    source, the poor quality of furnish as compared to virgin fiber, and a lower-quality

    product (6). Fractionation can help solve many of these problems. The long fiber

    component separated through fractionation theoretically contains mostly softwood

    fiber and contributes to strength properties. The short fiber component contributes

    to the smoothness and opacity of the sheet.

    How To Fractionating Secondary Paper

    By changing the normal operating conditions, pressure screens, centrifugal cleaners,

    and pulpers can be used. Other options for fractionation include source separation,

    selective pulping, and sccreening equipment, such as side-hill screens.

    An overview of industry-scale fractionation equipment concluded that screen

    fractionation and pressurized digestion are the most economically sound when

    considering the annual return on investment.

    A. Pressure ScreensPressure screens are an integral part of many stock preparation areas,

    especially in the secondary fiber area. In terms of the fractionation of fibers

    into long and short components, it was found that the geometry of the

    basket had an effect on the performance of the screen.

    Profiling the flow side prevented the formation of a filter mat and gave less

    distinct separation but more uniform suspension properties. Contour slotted

    screens reduced long fiber fractionation, decreased the reject rate, and

    reduced sensitivity to consistency and contaminant content. It was possible

    to achieve good separation with slotted screens at either high or low reject

    rates, where the long fiber fractions were considered the reject. However,

    with holes, good separation could only be achieved at low reject rates.

    The effect of hole size in the pressure screen on fractionation was shown by

    LeBlanc and Harrison where, as expected, increase the hole size increased

    the accepts flow, thus increasing the average length of the long fiber.

    When pressure screens are also used for contaminant removal, a

    competition exist between the fractionation and cleaning functions of the

    pressure screen. In the case of fractionating contaminated pulp, coarse

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    contaminants, as well as wax and hot melts, tend to be concentrated in the

    long fraction. Profile screens that induce a pulse into the stock flow reduce

    this tendency.

    A high proportion of long fiber can be achieved with a two stage screening

    cascade.

    B. Centrifugal Cleaners

    Centrifugal cleaners can also be used for fractionation of fibers and have

    been studied in some detail. However, in the centrifugal cleaners, hydraulic

    shear, hydraulic drag, density, and centrifugal force play a role in the

    separation of material.

    Fig. 5. Schematic flow motion in a hydrocyclone

    A hydrocyclone, also known as a centrifugal cleaner, has gained widespread

    use as classifying equipment due to its low energy and space requirements.

    During the operation of a hydrocyclone, Fig 5, the pulp suspension is

    injected tangentially through a feed pipe located near the top of the device.

    Under the influence of the centrifugal and drag forces generated by the

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    swirling suspension, a movement of the fibers relative to the water is

    produced. This relative motion between the fibers and the suspending fluid

    depends largely on the basic fiber properties.

    In general, cleaners tend to separate the pulp into flexible and stiff

    component. The cleaner underflow (rejects) tends to contain the longer-

    stiffer fibers that have a lower specific surface.

    The overflow (accepts) contains the well refined, more flexible fibers as well

    as the fines. Along these lines, a separation into springwood and

    summerwood fractions was achieved using centrifugal cleaners. This allows

    the stiffer fiber to be separately refined and then returned to the furnish,

    thus improving properties. Other investigations indicated that cleaners can

    separate based on specific surface area.

    However, as cleaners also affect contaminants, there is a difference in theimpurity content with the wax accumulated in the flexible fraction and

    aluminium foil concentrated in the less flexible fraction, although this may

    depend on the specific operating conditions.

    C. Fractionation Pulping

    Selective or partial pulping of the secondary fiber supply can lead to

    fractionation by fiber type or source. Selective pulping achieves separation

    by pulping to the point where the component of the recovered paper thatdefiberizes easier is sufficiently disintegrated so as to be removed from the

    remainder of the furnish through coarse screening.

    For example, under the proper mechanical, chemical, and time conditions,

    the medium of old corrugated containers (OCC) is reduced to smaller pieces

    than the linerboard, thus allowing a separation.

    D.

    Upgrading of stock preparation plants

    There are two main options for stock preparations plants. The first one consists of

    minimized cleaning and screening in the stock preparation plant without

    fractionation and without further fibre such as dispersion and further cleaning and

    screening. The second option comprises of fractionation and dispersion. After

    fractionation process, screening and heavy-and light-weight cleaning of the long-

    fibre fraction is applied.

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    Energy

    Savings

    Potential

    The option one results in energy consumption in the range 45

    kWh/tonne and 95 kWh/tonne. The second option consumes

    between 75 kWh/tonne and 175 kWh/tonne.

    Costs The investment and operational costs of option two are higher thanthat of option one.

    There might be different aims for upgrading of stock preparation plant concepts.

    They depend on the priorities set by a given company such as better removal of

    smaller impurities and contaminants to improve product quality and efficiency of

    the paper machine, enhanced recovery of fibres from rejects thus reducing the fibre

    losses, or energy savings. Another aim can be simplification of the stock preparation

    system resulting in less energy consumption, less material losses, and less spaceneeded. In order to simplify the stock preparation, especially for brown grades the

    possibilities for removal of energy consuming dispersion and traditional cleaning

    stages are discussed. In contrast, extended process concepts with a higher number

    of process stages might be used to manufacture paper for special purposes or to

    meet the customers needs (high-quality products).

    The processing of recovered paper targets first of all the removal of non-fibre

    components (e.g.plastics, metal, wood, sand) and the elimination of detrimental

    substances such as stickies, wax or small pieces of undisintegrated paper (flakes) of

    wet-strength paper. The second goal of pulp processing is the treatment of the

    fibres themselves to control the quality of the paper to be produced. To achieve this

    aim, fibres can be fractionated into long-fibre and short-fibre fractions and further

    treated. For example, low intensity refining improves the bonding ability of the

    recycled fibres, resulting in increased strength characteristics of the paper produced,

    and disperging improves the optical homogeneity of the paper.

    For each specific treatment of recycled pulp, special machines are used in various

    ways. Thus, the screening and cleaning processes must operate in two to four stages

    in order to reduce the fibre losses in the final stage of each process. To realise an

    adequate runnability of the paper machine it is also essential to operate additional

    cleaners and screens in the stock approach flow system. This prevents that deposits

    released from chest walls or from pipes enter the headbox and the wet-end of the

    paper machine. These deposits would lead to web breaks and downtime of the

    machine.

    A balance between cleanliness of stock, fibre losses, energy requirements and costshave to be found and are to certain extent depending on the paper quality produced.

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    In the following some of the different technical options for stock preparation plant

    concepts are highlighted including there major advantages and drawbacks.

    Implications for the electricity demand are indicated.

    Figure 6 shows four examples for stock preparation plant concepts for processing

    recovered paper for 2-ply testliner. This paper grade is used as an example because

    of its high importance in tonnage for paper and board mills in Europe and because

    information was easily available.

    Table 1 compiles for these four options the major characteristics, summarises the

    electricity demand, and gives some explanations concerning the lay out of the stock

    preparation plant. The figures for electricity demand for the four different systemsresult from the values for specific energy demand for single process units as

    compiled in Table 2 further below. They should be considered as a realistic

    approximation. Real mills might have slightly lower or higher values.

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    Figure 6. Four examples for stock preparation plant concepts for processing

    recovered paper for 2-ply testliner. [IFP, 1998]

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    Table 1. Major characteristics and electricity demand of different stock preparation

    plant concepts for processing recovered paper for 2-ply testliner. Some explanatory

    notes are given where considered helpful [Data derived from IFP, 1998].

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    Table 2: Specific energy demand and operating consistencies for unit processes in

    the production of Wellenstoff and Testliner [IFP, 1998; data according to a

    machinery supplier]; data refer to 100% efficiency]

    Applicability and characterisation:Process-integrated measure. Rebuilds of stock

    preparation plants as well as of the stock approach flow system can be usually

    realised in existing mills. A "standard" stock preparation plant typically uses moremachines than are required for this "minimised" stock preparation plant system

    (example 1). To adapt a "standard" system to a "minimised" concept, the shut down

    of only a part of the equipment is necessary and probably some new pipes and

    pumps for the connection to the machine chest are required. The stock approach

    flow system has to be extended. Existing screens from the stock approach flow

    system or from the stock preparation plant are usually not sufficient, due to the

    limited capacity when screen baskets with a narrow slot width of 0.15 mm are

    installed. Therefore, investments of advanced pressurised screens for the approach

    flow system would be necessary.

    Main Achieved environmental performance: The electricity demand for stock

    preparation and stock approach flow system is between 20 and 40 % of the total

    power demand of a recovered paper processing mill without de-inking. Therefore,

    optimisation of the stock preparation plant with respect to savings of electricity is

    worth considering. Reduced electricity consumption results in reduced air-borne

    emissions, which depends further on the type of fossil fuel used.

    The environmental advantage of the concept example 1 is related to savings of

    electricity for the stock preparation and the stock approach flow system. A system

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    installed in a German paper mill operates with an electrical power demand of 60

    kWh/tonne paper produced. For comparison: the mean value of the electricity

    demand given in the Table 5.25 below results in a power demand between 45

    kWh/tonne and 95 kWh/tonne (average 70 kWh/tonne) paper for the system shown

    as example 1. In comparison to a concept where screening as well as light- andheavy-weight cleaning of the long-fibre fraction after fractionation is applied

    (example 3) the energy demand of example 2 is reduced by 10 % to 20 % (65

    kWh/tonne 160 kWh/tonne).

    The main positive effect on the environment achieved by "extended" stock

    preparation plant concepts as example 4 is related to high paper machine efficiency

    resulting from a very clean pulp with improved strength characteristics.

    The electricity demand given in Table 5.24 above results from figures for specific

    energy demand of unit processes given in Table 5.25 below. As can be seen, the

    differences in electricity demand between the four options are significant: example

    4 (with all options) requires between 110 kWh/tonne and 270 kWh/tonne compared

    to 65 kWh/tonne and 160 kWh/t consumed by example 2.

    However, it has to be born in mind that improved efficiency of the paper machine

    that is achieved by cleaner pulp results in lower specific electricity and steam

    demands for paper production, because during breaks the paper machine still uses

    electricity and steam. In contrast, technologies that are connected with the need for

    more frequent system washing (downtime) decrease energy efficiency and increase

    emissions.Cross media effects:Paper machines running with increased efficiency have lower

    electricity and steam demands per tonne of paper. The improved recycled fibre

    quality results in an improved paper quality.

    The rejects from different process stages can be collected separately and used for

    different purposes. For example, rejects containing high amounts of plastics can be

    incinerated with the benefit of considerable energy recovery, due to their high heat

    values. Rejects with high amounts of organic fibre material can be used for

    composting. The rejects of the high-density cleaner as well as of the pulper disposal

    system usually are disposed of by landfilling because of their high content ofinorganic material (e.g. stones, sands, staples, clips, etc.)

    Operational data:World wide a large number of mills are producing testliner with

    fractionation and dispersion. Sometimes refining is also included in the stock

    preparation plant. Nevertheless, no exactly identical systems appear to exist.

    Example 1 as shown in Figure 5.15 can be regarded as a "minimised" stock

    preparation plant concept. It is running in one mill producing testliner and

    wellenstoff (Zlpich Papier Recycled Paper Europe, Germany). With respect to the

    achievable paper machine efficiency and local limitations this stock preparation

    plant concept has to be regarded as an experiment. Because of limited time of

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    experience it is not yet possible to evaluate the success of this energy saving

    concept. The system seems to result in slightly increased losses of fibres.

    Screening in a conventional stock approach flow system has predominantly an

    insurance against accidental contamination with low demands for maintenance. The

    maintenance required in the conventional stock preparation does not necessarilycontribute to a paper machine shut down because of the pulp storage capacity in

    available chests. In contrast, if finely slotted screen baskets (with a slot width of 0.15

    mm) are applied in the approach flow system in order to achieve sufficient clean

    recovered pulp (as in example 1) those screens require more extensive maintenance

    for cleaning. This results in a shut down of the paper machine and lost production.

    Therefore, the paper machine efficiency with the "minimised" stock preparation is

    normally poorer than that with a well equipped "standard" stock preparation plant.

    Economics: The investment and the operation costs of example 2 are lower

    compared to the example 3 and 4 and higher compared to the example 1 shown inFigure 5.15. However, increase of costs for the operation of the stock preparation

    plant has always to be evaluated in the light of improved paper machine efficiency.

    A lower number of shut downs and web breaks as well as improved paper quality are

    also important factors.

    Besides the higher investment costs for the equipment of "extended" stock

    preparation concepts (example 4), increasing operation costs in terms of the

    electricity demand for stock preparation have to be expected. "Minimised" stock

    preparation concepts (as in example 1) require relatively low investment costs. Low

    electricity reduces operation costs also.

    Driving forces for implementing this technique: The principal driving force for

    implementing stock preparation plant concepts with a higher number of process

    stages is the high quality requirements of the paper to be matched, which has to

    compete on the market with paper manufactured from virgin fibre. A further

    incentive is that paper machine runnability should be improved. The driving forces

    to implement stock preparation plant concepts with "minimised" process stages are

    lower investment and operation costs mainly savings of electrical power as a result

    of the fewer machines required.

    Example plants: Several mills in Europe are equipped with a stock preparation

    system similar to example 2 including fractionation and dispersion. However, the

    equipment installed and the number of process stages varies and no exactly

    identical system appears to exist. Some mills also have implemented a dissolved air

    flotation for process water treatment. The combination with washing as shown in

    example 4 has not been realised for testliner production so far.

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    E. Secondary separation pulper for pulping process in wastepaper treatment

    The pulper enhances pulping by causing wastepaper fibres to swell. The

    conventional process also pulverizes the impurities contained in the waste paper.

    These impurities are difficult to remove. The secondary separation pulper does not

    pulverize the foreign matter. The device continuously separates external matter and

    simultaneously performes the pulping function. Although the energy saving effect

    of the equipment itself is not very large, it makes a large contribution to energy

    saving in the downstream processes by eliminating the need for equipment for

    removal of foreign matter.

    The installation of this equipment also helps increase the mill capacity significantly

    (In one Japanese plant, capacity was increased from 365 to 445 tons per day with this

    technology)(NEDO, 2008.p. 159).

    Energy

    Savings

    Potential

    For a mill with original production capacity of 365 tpd, installation

    of this technology helped increase capacity to 445 tpd and reduced

    energy consumption by around 146 800 kWh/year (NEDO, 2008.

    p.160).

    Costs Equipment cost is estimated as 90 million. Construction cost is

    around 30 million approximately (NEDO, 2008. p.160).

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    Figure 8. Secondary Separation Pulping

    The pulper is a facility to facilitate maceration of collected wastepaper to form a

    slurry and to remove large foreign materials. The pulper swells fibers to promote

    maceration and adds a small amount of caustic soda to help remove inks when the

    paper treated requires deinking. Formerly, wastepaper was soaked in water at a lowrate of only several percent and vigorously agitated by a rapidly revolving impeller to

    achieve maceration by slashing; in such an operation foreign materials were

    crushed. The drawbacks were that the crushed foreign materials must be removed

    in the subsequent processes and the rotation and agitation consumed a large

    amount of power; in other words, the former process was very low in energy

    efficiency. The secondary pulper has been developed as a countermeasure against

    these drawbacks. The secondary pulper conducts preliminary maceration and

    continuously removes foreign materials without breaking them. Use of the

    secondary pulper could reduce the degree of maceration and hence could achieveenergy saving in the total operation of wastepaper processing.

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    In general, the pulper operation is either in batch or continuous depending on

    whether the liquor is at high concentrations or at medium concentrations,

    respectively. The operation consists in separating coarse raw materials and

    eliminating such heavyweight foreign materials as metals and feeding the coarse

    raw materials to the secondary separation pulper. The secondary separation pulperis equipped with punched plate screens and a rotating impeller macerator for

    preliminary maceration and removal of large foreign materials intact to finally send

    the treated material to the subsequent processes.

    Table 1 Effect of secondary separation fulper (Feed: Collected waste corrugated

    fiberboard)

    Energy saving effects :

    Addition of the secondary separation pulper could increase processing capacity by

    20 percent. However, it does not achieve energy saving in the maceration process

    alone. It could facilitate the subsequent dust removal operation by removing foreign

    materials without crushing them. For this reason, it has a great energy saving effect

    on the total processing of waste paper in this way.

    [Economics] Equipment cost :

    Investment amount (A): 80 to 90 million yen

    Improvement effect (B):70 million yen/year

    Investment payback (A/B): 1.2 years

    Remarks

    The average electric power consumption in the maceration process is 66 kW/ton

    when processing old newspaper including deinking and 52 kWh/ton when processing

    used corrugated fiberboard.

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    F. Continuous batch fibre recovery system to processing recovered paper

    The continuous batch fibre recovery (CBFR) system has the potential to improve the

    competitiveness of smaller mills and paper machines. It can process recovered paper

    materials in quantities as low as 3 t/d. The main objective is to provide mini recycling

    mills close to the source of recovered paper. The process combines several

    traditional processes that are used in recovered paper processing. Hence it

    eliminates several processes such as deflaker, washing, flotation, dispersion and

    kneader.

    The continuous batch technology is a connected modular system which provides

    for individualized process control of each module, controlled consistency transfers,

    and the elimination of most pumps and pipes to transfer fiber within the immediate

    direct system.

    Recent application of a more economical and related process technology has beensuccessful in recovering fiber from various classifications of recovered paper

    materials. A new continuous batch fiber recovery system has been developed

    which uniquely combines the individual stages of deinking technology, pulping

    through bleaching. The results indicate the potential for excellent recycled fiber

    quality while reducing energy consumption and equipment requirements. The initial

    trials focused on deinking newspapers and resulted in a 62 brightness and a 35 ppm

    dirt count from the processed materials.

    (http://www.tappi.org/Bookstore/Technical-Papers/Conference-

    Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspx)

    Pellerin Milnor Corporation, a leading manufacturer of commercial laundry

    equipment, has developed a modular fiber recovery system that is a variation of an

    established product line known as the continuous batch Tunnel Washer system. Due

    to the unique material transfer methods of the Tunnel Washer system, several

    process functions are combined in a single piece of equipment.

    It begin with prototype that consisted of one seven-module continuous batch

    Tunnel Washer system. Monitored functions included loading, pulping, separating,

    reject handling, screening, washing/thickening, clarification of liquid streams, and

    overall system fluid flow.

    This technology brief details the evaluation of a small-scale system for fiber recovery

    from milk carton/drink boxes (MCDBs). Pulp characteristics, effluent characteristics,

    and operating costs were monitored during the systems trial.

    http://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspxhttp://www.tappi.org/Bookstore/Technical-Papers/Conference-Papers/1995/REC95/Continuous-Batch-Fiber-Recovery-An-Economical-Alternative-1995-Recycling-Symposium-Proceedings.aspx
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    In Table below, the operating costs are extrapolated to compare a Tunnel Washer

    system processing MCDBs with a state-of-the-art deink system processing mixed

    office waste (MOW).

    References to operating costs include only variable cost and labor. Semi-variable

    costs (operating and maintenance supplies) and fixed costs (depreciation, taxes,

    salaried labor) are not included. The MCDB system is penalized for labor due to

    lower production capacity; however, the system is more cost effective than a state-

    of-the-art deink system for chemicals and energy. Effluent treatment and residual

    disposal are comparable between the two systems.

    The test system yield was 63.8% BDT to BDT (bone dry ton of feed stock to bone dry

    ton of pulp product) for postconsumer MCDB. For variable costs to be comparable to

    a state of the art, optimum sized, market deink pulp mill, the yield on milk carton

    would need to be approximately 73% BDT to BDT.

    Future Development : Further development work has resulted in significant optical

    property improvements: a dirt count of 10 PPM and debris level of 0.03%.

    G.

    Heat Recovery from De-Ink Effluent

    De-inking effluents are usually discharged at relatively higher temperatures and they certainly

    represent the possibility of low-grade heat recovery. The installation of heat exchangers in the

    effluent discharge system can recover some of this heat for mill uses such as plant water heating.

    EnergySavingsPotential

    For a mill in the US having effluent streams at 49 C and flow rate of 2.7m3/min, the installation of a heat exchanger to recover heat and generate warmfiltered shower for the mill's paper machines is estimated to reduce boiler fuelconsumption by 39 000 GJ/y.

    Costs Fuels savings for the boiler are estimated at $125,000/y. Capital costs hadbeen $375,000 with a payback period of around 3 years.

  • 8/10/2019 Recovered Fiber Pulping Note

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