Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION AND REVIEW OF THE PRIOR ART
Recycling of waste paper is possible only after
most of the non-cellulosic contaminants have been removed
from the fiber mass. These contaminants may have been
introduced during the printing steps (carbon black, pigments,
ink vehicles, ink fixating polymers, etc....), during converting,
(varnishes, coats, binders, wrapping, etc...) and later
during the collecting phase (metallic pieces, plastics,
soils and dirt of any kind).
Removing of the contraries generally occurs based on
chronological dimensional sequences, through screening,
magnetic separation, first in dry conditions and later in
aqueous suspension.
The fiber mass is then screened through perforated
plates and finer contraries are removed by centrifugal and
centripetal cleaners.
The ink particles are not substantially removed
during the proceeding steps, an this operation is
achieved in two steps: (a) detaching the ink particles
from the fiber surface, through the combined action of
chemicals, temperature and mechanical shear forces and
(b) removing these particles from the pulp slurry.
Generally, all the contraries including the ink
particles, are released from the fibers during the defibering
phase. The waste paper is treated in a pulper, under
alkaline conditions at 50-60C. temperature, in order
to be well defibered and transformed into a pump able
slurry. An alternative to this process is to operate the
pulper in cold conditions, then thicken the pulp above
15% consistency, then heat the pulp with steam at 60C.
introducing at that point the de-inking and bleaching
chemicals. The pulp then remains in a reaction tower
during 2-3 hours without any mechanical action.
The first drawback of these techniques is that all
contaminants are submitted to the thermal treatment,
including the ones which have low melting points, such as
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binders, hot melts, plastics and other "stickles". By this
way, they become dispersed and cannot be removed any more
by the conventional means, and will precipitate again on
paper machine elements such as doctor blades, wires, felts,
pipe walls, etc..., creating operating problems and loss
of efficiency.
A second drawback is that these ink-releasing techniques
have a weak action on the modern inks such as the rotor
offset inks, where ink vehicles are made of synthetic resins
which form an insoluble polymer onto the surface of the
fibers. The same consideration applies for xerocopy printed
paper and varnished papers, where temperatures in the range
of 60C. will provide neither any softening of the ink
vehicles nor any weakening of the bonding between the fibers
and these vehicles.
Another limitation of these techniques is that it
is not possible to increase the temperature of the ink
releasing step, because the combination of the alkalinity
and the temperature during a long time will result in an
unacceptable yellowing of the pulp, specially if some
grounded is present in the mixture to be treated.
Ink removing techniques in use to-day are essentially
two: flotation and washing.
In flotation , the diluted fiber slurry is intensively
mixed with air after a hydrophore ink collector has been
added. Then stock is naturally decorated and air bubbles
collect the ink particles during the upwards travel to the
surface. The resulting black foam is then collected and
treated separately through centrifuges, then skewered-
In washing, a very old and well known process, the
finest dispersed particles are removed through several
dilutions and squeezing cycles, generally arranged as a
counter-current cascade configuration. The effluent of
the first squeezing sequence contains all the free fine
ink particles, but also a great quantity of fine cellulosic
fibers and most of the mineral fillers, and are skewered
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and treated according to the local pollution regulations.
Some other ink removing techniques exist such as
solvent extraction but have not been followed by wide
industrial application, due to high production cost and
low quality of the produced pulp.
In the US. Patent N4,076,578 Pudding ton et Alp
recall the fundamental concept of de-inking: (a) releasing
ink from the paper fiber by means of chemico-thermo-
mechanical treatment and (b) separating of dispersed
ink particles from the pulp, then proposes a different
method to achieve this goal, through adsorption of the ink
particles onto the surface of solid particles, followed by
the removal of said particles from the pulp, and then
removal of the ink from those solids.
Nowadays, none of the above mentioned processes has
asserted itself because each of them presents some
drawbacks.
The flotation is a low consistency process (between
1% and 2%) and thus involves high volumes of pulp, with
consequent high investment cost. Also, the nature of this
process is essentially physico-chemical and thus its
stability is greatly related to the stability of the compost-
lion of the waste paper, the type of fibers (chemical or
mechanical), the type and content of mineral filler, the
calcium ion concentration. Consequently, the brightness
of the de-inked pulp shows undesired high fluctuations,
These brightness variations are also accompanied by all
composition variations coming together with the raw material
(waste paper), without any possibility of control or
continuous measurement and monitoring.
To-day, it is generally admitted that the first
condition for the good operation of a modern fast paper-
machine is the constancy of operating parameters, the most
important one being the composition of the stock feeding
machine. Unfortunately, it is not possible to control
the composition of a waste paper lot as easily as a virgin
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pulp bale. For this reason, the efficiency decrease of
high-speed paper machines using high percentages of
flotation de-inked pulp is mainly caused by the uncontrolled
variations of the stock composition rather than by the
brightness (or de-inking efficiency) variations. This problem
can be solved using selected classified waste paper, at a
price which makes the de-inked pulp uncompetitive respect
to the virgin pulp, assuming that such type of waste is
available.
lo Finally, the flotation process needs to be continuously
controlled, on a three shift basis, by highly specialized
chemical experts using sophisticated instrumentation and
laboratory, thus appreciably increasing the production cost.
The washing process involves simpler, cleaner, and
easier to control equipment, in particular when washing occurs
at consistencies between 3% and 15%.
This process does not require any specialized control
and it is admitted that not only the quality (cleanliness
and strength) of the washed pulp is definitely higher than
for the floated pulp, but this quality is much more constant
and less sensitive to raw material variations of composition,
thus offering a higher "tunability" of the pulp in the paper
machine room.
In fact, the principle of washing on a perforated
plate statistically says that elements having a smaller
size than the plate openings should pass through the
plate. It appears that the variations of composition of
the stock to be de-inked (fines, grounded, mineral fillers)
will reverberate on the fraction lost through the plate,
giving a final product almost constant in quality, if not
in quantity. This principle allows for the use of unselected
waste paper, a lower quality product having a much lower
cost and higher availability.
On the other hand, this process needs a much higher
quantity of water, and produces the equivalent higher
quantity of effluents which still contain a great quantity
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of valuable products cellulosic short fibers mineral
fillers, mixed together with the undesired ink. Besides
that direct loss, it is necessary to consider the us-
direct cost due to the abatement of the pollution created
by the solids contained in the effluents.
In conclusion, it can be said that if flotation de-
inking presents high investment and operating cost together
with low constancy of the quality of the final product,
washing de-inking also shows a high similar cost of the
product due to both the intrinsically low yield of the
process and the pollution abatement cost.
In order to minimize the negative aspects of each one
of these basic processes, their supporters have proposed
several combinations of them, keeping in mind to produce
only one de-inked pulp starting from one waste paper
mixture.
In the French Patent Application N79 19392, M. Fritz
Zebu of Voith Cry. suggests to remove the fine fibers
fraction together with the mineral fillers from a flotation
de-inked pulp, using screens and strains arranged as
washing elements. This process, which is only summarily
described without any example, seems to add up both costs
and drawbacks of flotation and washing.
In the TAIPEI magazine, vowel, N9, September 1980
M. Luther Pfalzer of the same Voith Cry., while recalls
the same concept (page 116, fugue), specifies that the fine
fiber fraction and mineral fillers are centrifugated and
then skewered and lost. It also appears from this publication
that the effluent is totally sediment Ed after having been
flocculated by addition of aluminum sulfate, but it is
also specified that a good dispersion of the ink particles
can be obtained at high and well controlled phi
These two statements are rather contradictory and make
this concept hardly applicable in practice,
M. Pfalzer also suggests the opposite philosophy
(page 114, foggily), which consists of a total flotation
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followed by a total sedimentation of the effluents of
a conventional washing process. For the same reasons as
above, which are: the low yield of the washing process,
the non-compatibility between ink dispersing high pi and
aluminum sulfate sedimentation low phi the addition of
the costs and drawbacks of each individual process, this
proposal has not been applied on an industrial scale.
In the French Patent Application N78 29637, M,
Calumniate of Montedison Cry. suggests in a more simple
way to separate the ink particles from the fine fibers
and the mineral fillers contained in the effluents of
a washing process, by means of a simplified flotation
process where no chemicals are added. It is also stated
that the chemicals added at the beginning of the process
(pulping stage) will also provide for the ink collecting
function. In this process, the suckled "clarified"
effluents which actually contain most of the fibers and
mineral fillers lost during the washing step, are totally
recycled ahead of the process.
A tentative application of this process had to be
quickly abandoned for two reasons. At first, it has not
been possible to obtain a satisfactory selective removal
of the ink during the flotation, because of the antagonistic
functions of the two chemicals mixed together at the pulper:
(a) dispersing of the ink needed during washing, (b) keg-
lotion of the ink needed during flotation, So, too much
fibers and fillers were floated together with the ink
resulting in a quick overloading of the sewer system,
and immediate shut down of the plant.
At second, it has not been possible to recirculate
continuously-ahead of the washers, an effluent which
contains most of the fines and fillers lost by the same
washers. This total recirculation has quickly resulted in
(a) a drop of the brightness due to the poor ink removal
efficiency and (b) an unacceptable drop of the hydraulic
capacity of the thickening elements. Both can be attributed
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to the saturation of the circuit with fines and fillers,
dimensions of which are of the same order of magnitude
than the ink particles.
In the Italian Patent Application N26344 A/80,
M. Calumniate recalls the same principle, where the effluents
at a concentration of 0.14% would be selectively floated
with the only addition of air, and then totally recycled
ahead of the process together with their suspended solids.
M. Calumniate nevertheless suggests to install a "quick"
flotation, a third flotation, installed ahead of the washing
process. This configuration does not seem to bring any
answer about the two basic previous problems; (a) how
is it possible to have the best dispersion together with
the best coagulation, (b) how is it possible to avoid
the saturation, the clogging of the thickening elements,
and the loss of the ink removal efficiency, due to the
recirculation of the fines and the fillers together with
the effluent.
GOALS OF THE INVENTION.
The present invention aims to provide a practical
and integral industrial process which allows to produce,
in a continuous way and starting from a mixture of
unselected waste papers, three separate products, namely:
a) a totally cleaned and de-inked pulp having constant
and controlled brightness and fiber classification,
having a very low and constant fillers content;
b) a totally cleaned and de-inked pulp having a
fine fiber classification and a very high fillers
content, these two parameters being variables both
quality and quantity;
c) an effluent which does not practically contain
suspended solids, which has not been submitted to
any pi reversion, which does not contain any flocculation
or sedimentation chemical agent, and thus is
immediately and totally reusable as the dilution
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and washing liquid during the ink removal step of
the de-inking phase.
A further aim of this invention is to provide
a practical and advantageous improved method for de-inking
these grades of printed papers and boards which cannot
be correctly de-inked by conventional methods.
Another aim of this invention is to provide
a practical and advantageous method which allows to
produce high quality paper and board at high speeds
using the low quality waste grades which could not be
used for such noble purpose when treated by conventional
methods.
The invention is also directed to the application
of modified and purposely adapted ink removal processes !
such as washing, selective separation, flotation, coagulation,
filtration, onto the high ink-content slurry produced by the
primary itik removal process.
The invention also aims to allow for the use in
paper making of the by-products of a washing de-inking
process, either on the paper machine which will use the
primary pulp, or on a different paper machine.
An object of this invention is to provide a means
to create a constant and controlled composition of the
pulp used for paper making, which can be different from
the composition of the incoming waste paper mixture,
This object is achieved by pumping controlled flows
of each one of the two components and mixing them ahead
of the paper machine(s) in the desired percentage; the
capacities of the chests act as buffers between waste
paper and paper machine stock compositions.
Another object of this invention is to increase the
value of the by-product (the secondary pulp) by the fact
that good long fibers can be extracted from the main line
in order to optimize the operation both of the selective
separation of the ink and of the filtration on fiber mat.
A further object of this invention is to accomplish
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the selective separation of the ink at a stage where this
ink is highly concentrated (approximately three times more
than in the main pulp), thus increasing the efficiency of
the chemicals.
An ulterior object of this invention is to achieve
the selective separation of the ink (which is the more
delicate operation of the whole recycling process), in
a satellite circuit of reduced capacity (approximately
one third of the flow through the main line), thus being
easier to operate and requiring lower investment cost,
This invention then aims to ensure the highest
possible constancy of quality of the primary pulp, by
the fact that the variations of fines and fillers contents
will instantaneously reverberate on the fraction produced
by the satellite circuit, which in turn can also be
stabilized by means of a thorough mixing and high retention
time in the final buffer chest,
With these and other aims and objects, the nature
of which will become more apparent, a fuller understanding
of this invention will be gained by reference to the following
detailed description and the appended claims.
SUMMARY OF TIE INVENTION
According to one aspect of the invention there is
provided a method of treating a mixture of printed and
contaminated waste paper in order to produce pulp for
use in the manufacture of pulp and paper boards, which
method comprises: (a) forming an aqueous pulp of the waste
paper at low temperature and low specific mechanical
energy, thereby forming a palpable slurry, and releasing
non-ink contaminants from the surface of the waste paper
but without dispersing the released non-ink contaminants
throughout the resulting fibrous suspension; (b) separate
in the non-ink contaminants from the pulp by mechanical
separation, without the use of froth flotation, solvent
extraction or other chemical]. process, using conventional
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screens and centrifugal cleaners and without any further
application of strong shear forces to the pulp; (c)
softening ink particles and weakening their bonds with the
surface of the fires by submitting the pulp at a consistency
of more than 15% to the simultaneous actions of (i) a
temperature between 85 and 130C, (ii) high shear forces
and (iii) at least one de-inking agent, under alkaline
conditions; (d) detaching the ink particles from the
surface of the fibres'and dispersing them into the fibrous
'suspension by submitting the pulp to the simultaneous
actions of (i) and (ii), as defined in step I and
(iv) at least one chemical dispersing agent, under alkaline
conditions; (e) removing the free ink particles to obtain
the degree of brightness required by the final use of the
pulp.
According to a further aspect of the invention there
is provided a method of treating a mixture of printed waste
paper in order to produce pulp for use in manufacture of
paper and board, which method comprises: (a) forming an
aqueous pulp of the waste paper; (b) removing non-ink
contaminants from the pulp and releasing ink particles
from the surface of the pulp fibers to obtain the degree
of brightness required by the final use of the pulp; (c)
removing ink particles from the remaining dispersed fine
material of the pulp using at least one washing stage
under alkaline conditions and in the presence of at least
one ink dispersing agent, thereby producing: (i) a primary
pulp having controlled and constant brightness and fiber
classification with very low and constant filler content
and (ii) a secondary pulp containing a variable high
filler content and a variable quantity of fine fibers,
together with the ink particles and some clean fibers; (d)
mixing the secondary pulp (ii) with an ink-collecting
hydrophobic agent, after the ink-dispersing agent has been
neutralized or precipitated, under alkaline conditions, and
then removing the ink particles from the effluent by
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selective separation of the hydrophobic agent from the
fibrous suspension; (e) reducing the alkalinity of the
slurry by addition of non-caustic insolubilizing cations
and a strong mineral acid, thereby producing a filterable
slurry; (f) filtering the fibrous suspension at a low
filtering rate on a fibrous mat composed of fibers coming
from the same process, thereby producing: (iii) a secondary
de-inked pulp having a fine fiber classification and a very
high filler content, both instantaneously variable, and (iv)
an effluent which is practically free of suspended solids;
(g) diluting the pulp thickened by the last but one
washing stage with the clarified effluent of step (f)
thereby conserving the water used in the method; and (h)
storing the filtered secondary pulp in a vat for several
hours with intense mixing by agitation and recirculation,
thereby leveling off the fluctuations of the filler content,
the fiber classification and the freeness.
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DESCRIPTION OF THE INVENTION
The following detailed description, together with
the attached schematic flow-sheet, refers to one preferred
practical application of the invention, although other
procedures can also be applied.
Following the flow-sheet, the bales of waste paper
are loaded into a pulper (2) by means of a loading mocha-
noisome, together with the recycled water and eventual caustics
in order to bring the pi at values above 7. It is possible
but not mandatory to introduce part or all the quantity
of dispersing chemicals required by the ink-releasing
action, during -the pulping operation.
The pulp is then diluted using recycled water and
pumped through one or several stages of screens and cleaners
(3) in order to release contraries and contaminants from the
paper surface, and further remove them from the pulp slurry,
When the de-inked pulp is used for high quality paper
production or on high-speed machines such as light weight
coating base or newsprint, this operation must be done in
the same way it is done with chemical or mechanical virgin
pulps, using the same equipment and operating parameters.
In particular, the best results have been obtained through
a combination of pressurized slotted screens equipped with
0.3mm, slot width working at I consistency followed by
4 inches size cleaners working at 2.8 bars pressure drop
and 0.6% consistency in the first stage.
It is anyhow of paramount importance that the temperature
of the stock is kept as low as possible so that the low
melting point contaminants will remain rigid and will not
extrude through the slotted screens and thus be eliminated
by the screens, This pulp is then thickened (4) to the
consistency required by the ink releasing process. The
effluents produced by this thickening stage can easily be
recycled, as they are cold and do not contain much fibers
and very little ink. At the beginning of the following
ink-releasing step (5) chemicals are mixed together with
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the fiber suspension. Caustics are added in order to raise
the pi up to 9-10, together with oxidizing agent (such as
hydrogen peroxide), and stabilizers (such as sodium silicate,
and dispersing agents (surfactants, eta,.,). The basic
parameters of this process, - temperature, pressure, specific
energy, chemicals dosing - will be determined in order to
ensure the optimum detachment of the ink particles from the
surface of the fibers together with their finest dispersion
inside the pulp.
In the hollowing examples, this operation has been
made in a kneader, also called triturator, which permits
to bring the temperature at the desired value (ire. above
the melting point of the ink vehicles) within a few seconds
and simultaneously apply very strong shear forces at high
consistency and in presence of de-inking agents,
The principle of the operation is that at first, the
combined actions of ink-releasing chemicals and temperature
(90-130C) will soften the ink vehicles and weaken the
bonding between the same and the fibers, and then the
combined actions of ink-dispersing chemicals and intense
shear forces will detach and finely disperse these particles
inside the fiber suspension. The high consistency (20-30%)
allows to treat very low volumes of pulp in small machines
during a very short time (2-3 minutes), thus avoiding the
yellowing of the pulp and increasing the efficiency of the
chemicals.
This pulp then remains 5 to 20 minutes in a latency
chest (6), at a consistency between 2% and 5%. It may then
be deflated in order to well separate the fiber bundles
one from the other, and thus facilitate the ink removal from
the slurry.
The fibrous suspension finally goes through the ink
removal process (3) which can be advantageously composed
of multistage counter-current, high consistency washing,
The number of stages is chosen according to the quantity
of ink to be removed and to the desired final brightness.
The extraction of the water is conducted through strains
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or perforated plates, the dimensions of the openings of
which will be selected in order to allow for a given
quantity of fibers to be carried away together with the
effluent, thus ensuring the optimum operation of both the
following ink selective separation process, and the final
filtration of the recovered satellite secondary pulp.
In case a filler-free secondary pulp is desired! the
effluents from the washing step (8) can advantageously be
strained again on one or several fine mesh filters (9),
By this mean, it is possible to remove at each filter stage
up to 80% of the mineral fillers contained in that slurry,
In such a case the finest fraction must be sent to a
conventional alkaline clarifier (10) and then skewered, The
clarified fraction is then returned ahead or after the
following ink selective separation step (11), according to
the operating parameters of this last process (consistency,
temperature), and according to the required brightness,
The necessary chemicals are also introduced ahead of
this step. In case this process is a selective flotation,
ink collectors such as fatty acids or their sodium or
calcium soaps can be added, taking care to ensure a mixing
time of about 5 minutes at a temperature of about 35 to 45C.
It may be worthy to recall that the dispersing agent
used during the washing step has a negative effect both on
the coagulation produced by the collecting agents during
the flotation step, and on the trainability (freeness) of
the fibrous suspension during the filtration step. It will
be good to inactivate or neutralize these agents for example
by precipitation with calcium chloride or calcium hydroxide,
The precipitation of the sodium silicate will also contribute
to increase the brightness of the secondary pulp through
the formation of a precipitated mineral filler It has also
been observed that the quantity of mineral fillers removed
together with the foam during the flotation step may vary
from 30~ up to 70% according to the operating parameters of
the process: flotation time, temperature, pulp consistency.
dosing and type of chemicals. The rejected foam containing
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the ink is then pumped to centrifuges or filter-presses and
skewered. The loss of solid particles has been observed to
be between 10% and 20% of the flow of secondary pulp, which
means about 3% to 6% respect to the total quantity of pulp
feeding the washing step (8).
It has also been observed that the maximum efficiency
of the ink removal has been reached at much higher consistencies
than the ones recommended by the suppliers of the cells.
For example, a cell designed to work at 1% has shown best
results between 1.5% and 2%. This peculiarity allows for
the treatment of lowest quantities of effluents, using
higher consistencies during washing, and larger holes in
the extractors perforated plates.
When the requested concentration for the ink selective
separation process is higher (say 0,5% or more) than the
maximum concentration which can be given to the effluent of
the washing step, some heavy stock can be advantageously
extracted from the latency chest (6). In this easel the
small quantity of long fibers added to the secondary pulp
will help in forming the filtering mat the final filtration
step (12).
The selective separation of the ink (if) can also be
a process based on adsorption of the ink upon the surface
of non-soap solids, as recommended by Ire Pudding ton et Al,
in the US. Patent N4,076,578.
The de-inked slurry leaving the process (if) is then
filtered on fibrous mat up to at least 4% consistency,
possibly above 10% in order to remove from the final secondary
pulp the maximum possible quantity of dissolved salts.
In case this pulp contains a very high quantity of
grounded fines and fillers (such as mixtures of newsprint
and magazine paper), the pi ahead of the filtration step
has to be dropped down to values below 8, by addition of
sulfuric acid (preferably to aluminum sulfate), under
intense mechanical agitation (as could be the suction side
of a centrifugal pump), and after some long fibers extracted
from the washed final primary pulp has been added to the
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satellite slurry to be filtered.
It has been observed that the application of equipment
such as Polydisk or Waco Filters to the thickening process
(12) has permitted to produce clear filtrate having less
than 100 Pam suspended solids and consequently totally
reusable in the pulping (2), cleaning (3) and washing (8)
processes without any further clarification.
The final thickened secondary pulp leaving (12) must
then be brought to a pi compatible with the following use
- by addition of sulfuric acid or aluminum sulfate always
under intense mechanical agitation, and can be stored in
a buffer chest according to the final use.
EXAMPLES
The following examples will illustrate three
different applications of the general procedure previously
described, using different mixtures of waste paper and
producing different grades of paper and board, Measurements
of brightness were made with an Elrepho* meter with 457nm
light filter, according to ISSUE. standards, Chemical
dousings are expressed in percent by weight of the chemical
at 100% concentration respect to the weight of total solids
in the line where said chemical is added. Sodium silicate
is considered at 38 Be and the Removing* F and L as supplied.
EXAMPLE 1
The raw material is a mixture of over-issued news-
papers and telephone books (white and yellow pages) in a
ratio approximately 50/50. The de-inked pulps are used for
t-he production of newsprint and telephone directory papers
(white and yellow), on only one high speed paper machine,
In this installation, the pulper has a capacity of 46m3
containing 2.700 kg of waste paper, Each batch longs 30 mint
Dilution water is coming from the effluent of the thickening
process (4) and make-up is made using clear filtrate from
the Polydisk filter (12), One percent of sodium hydroxide
is added in the pulper together with 1% of a de-inking agent
' ~,~; 'Allah * trade mark
Lowe
such as Removing L 8001 supplied by Chemicarta Swag Milan,
When this cold pulping operation is finished, the stock
is pumped through turbo separator, screens and cleaners, at
consistencies starting around 4% and ending at about 0.6%,
The turbo separator is equipped with a perforated
plate having 3mm. diameter holes and the rejected stock
is then sent to a vibrating flat screen also having 3mm.
holes, rejects of which are skewered.
The accepted stock from the turbo separator is then
diluted from 3% down to 1% before it passes through pressurized
slotted screens fitted with 0.30mmt slot width. The rejected
stock is processed through a second stage screen having the
same slot size, and rejects of the same go to a vibrating
flat screen, rejects of which are Seward
The accepted stock from the first stage of screens
is then diluted down to 0.6% consistency and processed
through a conventional battery of 4 stages of Triclean
cleaners. The light and the heavy rejects of the Thea stage
are skewered.
The total loss of both high and low consistency
turbo separating, screening and cleaning is varying between
6% and 9% by weight, depending upon the degree of contamination
of the waste paper. No more stickles or hot melts can be
seen in the pulp, and the eye inspection is confirmed by
the Somerville test, which shows less than 0.2% of shrives.
At that point, the pulp is totally cleaned and the only
remaining contaminant is the printing ink. The pulp is
then thickened up to 30% consistency in two steps, using
a disk filter up to 10-12% and then a screw press up to
30%. Characteristics of the pulp are: Britons ISSUE
frowns SR, filler continuity%, temperature=20-25C.
The ink releasing step (5) is achieved in a kneader under
the following operating conditions: temperature C,,
sodium hydroxide= 1.5%, sodium silicate= 4%, hydrogen peroxide
= 1.8%, specific enrage KW.H/Ton during 3 minutes The
brightness of the pulp at the end ox the treatment is
* trade mark
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ISSUE, and freeness is 60-65SR. The pulp is then
diluted using all the flow of effluents coming from the
second stage of washers, then squeezed up to 12% in the
first washing stage.
These washers are composed of inclined screws (better
known as Rice-Barton or Baker's screws), where the pulp is
drained under continuous and vigorous agitation through
perforated plates having 1.4 mm. diameter holes, in order
to produce an effluent having approximately 0.8-1% consistency,
The thickened stock is then processed through two other
similar counter current washing steps and the final usable
pulp presents the following characteristics: brightness=59-60IS0,
freeness=46-50SR, filler content 2-3%, consistency%.
This pulp represents 78% by weight of the quantity of pulp
feeding the washers (8). The balance 22% is going to the
satellite circuit with the first stage effluent which shows:
brightness=3S-40IS0, filler continuity%, freeness=80SR.
The capability for the ink of being removed from the
fibers contained in the effluent has been verified in the
laboratory as follows: an effluent sample has been hyperwashed
under fresh water shower on a 200 mesh wire, and a hand sheet
has been made, showing a brightness of ISSUE, which is
very similar to the brightness of the final primary pulp.
This effluent has then been mixed together with 4% of a
special ink-collecting agent purposely designed for this
application by Chemicarta SPA, Milan, and kept for 5 min.
under agitation at 30C.
The mixture is then processed through one single
stage conventional flotation cell, Voith open type, during
15 min. The loss of weight through the cell is 15-20%,
which means only 3-4, 5% respect to the total quantity of
pulp entering the washers. We have found that addition
of 0.5% to 1% of calcium chloride or calcium hydroxide together
with the collector, ahead of the flotation, helps controlling
the foam and the ink coagulation when low ash content pulps
are processed.
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The total alkalinity is then dropped down to pH=7-8
with addition of 1% of sulfuric acid on the suction side of
the centrifugal pump feeding the disk filter (12) At this
point, the pulp shows a brightness=53-56IS0, a filler content
=15-20~ and a freeness=78-80SR.
The disk filter (12) is a Polydisk filter sized
according to a specific filtering factor liters/min.lm2.
Besides this unusual value, it is also necessary to feed
the mat-peeling showers with air instead of water, in order
to reach the maximum possible consistency of the discharged
pulp .
Using the above mentioned parameters, a final consistency
of 8% to 10~ could be obtained and the clear filtrate
shown less than lOOppm average suspended solids, measured
on paper filter, black label.
The pulp is then brought to phi and sent to a buffer
chest having 8 hours total retention time. From this point
it is then pumped to the mixing chest of the paper machine
at controlled flow rates according to the paper grade
actually produced and in function of the mean composition
of the secondary pulp.
The clear filtrate from the Polydisk filter is then
totally recycled in order to dilute the stock ahead of
the third washing stage and make-up is provided by fresh
industrial water which does not contain aluminum ions.
The application of such a process in a paper mill
having one single paper machine is offering the following
advantages:
appeasability to maintain constant freeness and ash
content during a grade run, independently from the
incoming waste paper characteristics, thus allowing
the paper machine to run at maximum speed and
efficiency;
possibility to achieve very quick grade change,
exactly as when using virgin pulp and fillers, without
the need to intervene a long time before in the waste
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paper plan, thus permitting an easier and more
constant operation of that plant;
possibility to always use the highest possible
quantity of recycled fibers in the paper, by the
free disposal of each one of the two fractions and
their use in the optimum way,
possibility to produce totally cleaned pulps having
the same standards of cleanliness than virgin pulps
and thus offering the highest possible tunability
in the paper machine room, particularly being free
of any "sticky" or ought melt" or ink vehicle free
particle.
EXAMPLE 2
The raw material is a mixture of printed continuous
stationary, old books and office file, in a ratio 50/50.
The dunked pulp is used to produce, on three distinct
paper machines: (a) light weight machine glazed wrapping
papers, (b) fine papers for writing and printing, including
wood containing printing grades, (c) stationary and
continuous print-out papers,
The operation is similar to example (1) up to the
thickening step (4), although it is not necessary to add any
chemical agent - caustics or de-inking agent - during the
pulping step (2). Inn entering the ink-releasing step I
the pulp has a brightness=60IS0, a freeness=40-45SR, and
a filler continuity%.
The ink-releasing equipment is the same as for example
(1) but operating parameters are as follows: Removing L8001=
0.3~.; hydrogen peroxide%, sodium hydroxide%, sodium
silicate= 3%. All other parameters remain unchanged. At
the end of the process, the pulp has shown a brightness
increase of 2 ISSUE and freeness did not show any appreciable
variation.
The pulp is then washed by means of three washing stages
as for example (1), but the design of the perforated plates
are different: the first stage is fitted with 2mm. diameter
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holes, the second and the third stages are equipped with 1.4mm.
diameter holes. Also the feed consistency of the washing stages
is different, being 2.5%. With these parameters, the final
washed primary pulp has shown the following characteristics:
brightness=75IS0, filler content below 3%, freeness 27-30
SR.
The effluent leaving the first washers has a consistency
between 1% and 1.2%, a filler continuity%, brightness=50IS0,
and freeness=70SR.
The flotation cell used in this application is a high
consistency Sumac type, and heavy stock has been pumped
from chest (6) and mixed together with the effluent before
the flotation in order to raise the consistency up to 1,5%,
In this way, the two lines (primary by washing and secondary
by flotation) have exactly the same solids flow rate, or
the same capacity in tensed but produce two pulps having
opposite characteristics. This extraction also procures
long fibers which will help the final filtration (12),
This extraction could have been done using washed pulp
and this would have increased the brightness of the secondary
pulp. But in such a case, the washing equipment would have
to be sized for 30% more capacity, which is not a worthy
choice in our case.
The flotation is then conducted with only 2% of the
same collector (Removing F) and the retention time through
the cell is only 10 min., thus producing a loss of weight
of 10% (which means 5% of the total pulp).
After acidification at phi ahead of the disk filter,
the pulp shows a brightness=70IS0, a filler continuity%,
a frenzies.
The Polydisk filter can be sized using a filtering
factor = 25 liters/min./m2, and produces an effluent containing
70-100 Pam suspended solids. The other steps of this
application are similar to the ones described in example (1),
The application of such a process in a paper mill
having several paper machines as in this example is offering
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-22-
the following advantages:
appeasability to produce a pulp having physical and
cleanliness characteristics similar to the ones of
a virgin chemical pulp, thus usable for the production
of fine light weight papers, with good Yankee dryer
glazing capabilities;
possibility to produce a pulp having physical and
optical characteristics of a mixture of fine chemical
and/or grounded pulp, and mineral fillers, thus
usable for the production of printing papers where
high opacity and smoothness are requested,
possibility to mix these two pulps together in a
ratio which can be very much different from the
original one coming together with the raw material.
EXAMPLE 3
The raw material is a mixture of low quality printed
waste, containing old books, office waste and stationery,
and some newspapers and magazines, in variable proportions.
The mill has one multiple board machine, and procures
high quality folding box board, which can be on-machine
coated and must show an excellent multicolor offset
printing aptitude. The white top liner is composed of 100%
de-inked primary pulp and the underliner uses the secondary
pulp, mixed with other pulp.
Pulping is conducted in a continuous way with the tame
parameters as for example (1). The cleaning and screening
treatment (3) is simplified and composed of centrifugal high-
density cleaners, followed by a turbo-separator, working
at 3% consistency. The following thickening stage is also
simplified and composed of inclined screws producing pulp
at 15% consistency, followed by a screw press. The finest
contaminants will be detached and better dispersed during
the ink-releasing step (5) and then carried away with the
effluent during the washing stage. They will remain in
the secondary pulp thus contributing to add weight and volume
to the board, as the underliner does not need to be particularly
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cleaned.
The pulp entering the ink-releasing and dispersing
step shows a brightness ISSUE, a filler content =25-30%.
The operating parameters are the same as for example (1),
but the brightness drops down to ISSUE.
The following washing step has only two stages, which
are fed at 2.5% consistency, The perforated plates of
the inclined screws have 1.6mm. diameter holes, and it has
been found that the characteristics of the effluent are
very similar to the one of example (1),
The washed primary pulp shows a brightness ISSUE,
a filler content =4% and a freeness =45-50SR. The fine
cleaning of the primary pulp is achieved with the cleaners
and the screens installed ahead of the board machine, which
is sufficient to reach the desired quality, It must be said
that the contaminants have been thoroughly dispersed in the
kneader (5) and most of them have left this primary pulp
during the washing step.
The satellite circuit is also simplified because the
brightness of the underliner has only a third-order influence
on the final brightness of the coated board, We have observed
that a brightness of the underliner secondary pulp in the
ISSUE range was sufficient to ensure the required brightness
ISSUE of the coated board providing that the top liner
primary pulp has ISSUE, Thus, the flotation time has
been reduced below 10 mint and the dosing of the collector
has been kept below 2%. We have also observed that it was
possible to run without any chemical when lower quality
grades are produced, but no compromise can be applied on
the dispersion effect, because black spots in the under_
liner are always visible even through the coated top liner.
The application of such a process to the production of
stratified board is offering the following advantages:
appeasability to totally replace chemical pulp or
high quality selected unprinted waste paper by a
low value and large availability raw material;
~LZZ9~
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simplification of the main line by eliminating
the fine screening and cleaning equipment;
conquers of the total yield, by transferring in the
secondary pulp (and then in the underliner or in the
middle ply) all finely dispersed contaminants which
are not acceptable in the top liner,
