Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND MEASURING DEVICE FOR MEASURING RECYCLED FIBRE PULP
FIELD
[0001] The invention relates to a method and a measuring
device for measuring recycled fibre pulp in a recycled fibre process.
BACKGROUND
[0002] A recycled fibre line is also called an RCF line (ReCycled Fi-
ber), and it refers to a production process by means of which raw material for
printing paper is produced from wastepaper mainly for newspapers and maga-
zines. The process may also be called de-inking. Pasteboard and paperboard
may also be recycled and reused in a corresponding manner. The aim in the
pulping, washing, dispersing and rewashing of the recycled fibre pulp process
is to detach the fibres of the recycled fibre pulp from each other, to
separate
substances, such as printing ink, wax, glue, plastic, metallization etc.,
added to
the paper at the different stages from the fibres, and to remove the added sub-
stances from the recycled fibre pulp. The processing is complicated by the
fact
that the quality of recycled paper varies according to from where and how the
paper was collected. In addition, wastepaper contains impurities and its mois-
ture content varies.
[0003] A sample may be taken from the recycled fibre process and
subject it to hyper-washing, wherein the aim is particularly to remove ink pre-
sent as free particles in the sample. Hyper-washed samples taken at the dif-
ferent stages of the recycled fibre process may be compared with the recycled
fibre pulp at the different stages of the recycled fibre process, thus
enabling the
determination of the efficiency of the processing of the recycled fibre and
the
quality of the recycled fibre pulp.
[0004] Hyper-washing may be performed as a manual wash by tak-
ing a sample into a container of the desired size, on the bottom of which is a
wire. However, different laboratories use different wires, usually between 50
to
200 meshes (aperture size about 70 pm to 300 pm). The sample on the wire is
subjected to water rinsing, whereby the particles smaller than the mesh size
of
the wire flow out of the container.
[0005] A plurality of problems is associated with manual washing.
For example, containers, wires, numbers of samples, the temperature of the
rinsing water and the pressure of the rinsing water are different in different
measurements (made in different locations), which results in the measure-
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ments not being comparable. In addition, conceptions of a properly or
correctly
performed hyper-wash vary depending on the manner of measurement and the
performer of the measurement, although the washing time and the amount of
water consumed are known to affect the end result.
[0006] Hyper-washing may also be performed with a device manu-
factured for this purpose. In this solution, too, a wire (between 50 and 200
mesh) is used, through which the pulp is filtered by means of running water.
An
image-processing program may be used to measure both the loose ink in the
filtrate and the ink adhered to the fibres of the washed pulp.
[0007] Problems are associated with this solution, too. The material,
manufacturing geometry and wear of the wires affect the filtration and, conse-
quently, the measurement result. The manufacture and maintenance of identi-
cal wire geometries is impossible, since even microscopic differences in the
wires affect the measurement, and the manufacturing geometry changes along
with wear. In addition, since one sample may be measured only with one wire,
the result obtained from the sample cannot be compared with measurements
made on different wires. The reproducibility of the solution is not either
very
good.
BRIEF DESCRIPTION
[0008] It is the object of the invention to provide an improved
method and a measuring device implementing the method.
[0009] This is achieved with a method of measuring recycled fibre
pulp, in whose manufacture at least one of the following was used: paper, pa-
perboard, pasteboard, at least one added substance having been transferred
to the surface of the paper, paperboard, pasteboard. The method further com-
prises taking a sample from the recycled fibre pulp of the recycled fibre proc-
ess into a fractionating pipe, arranging the particles of the flowing sample
in
the fractionating pipe in accordance with the particle size, processing the
sam-
ple as at least two fractions according to the particle size, and measuring at
least one parameter of at least one added substance in at least one fraction.
[0010] The invention also relates to a method of measuring recycled
fibre pulp, in whose manufacture at least one of the following was used:
paper,
paperboard, pasteboard, ink having been transferred to the surface of the pa-
per, paperboard, pasteboard. The method further comprises taking a sample
from the recycled fibre pulp of the recycled fibre process into a
fractionating
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pipe, arranging the particles of the flowing sample in the fractionating pipe
in
accordance with the particle size, processing the sample as at least two frac-
tions according to the particle size, and measuring at least one parameter of
the ink in at least one fraction.
[0011] The invention further relates to a measuring device for
measuring recycled fibre pulp in a recycled fibre process, in whose manufac-
ture at least one of the following was used: paper, paperboard, pasteboard, at
least one added substance having been transferred to the surface of the pa-
per, paperboard, pasteboard. The measuring device comprises a fractionating
pipe arranged to receive a sample from the recycled fibre pulp of the recycled
fibre process and to arrange the particles of the flowing sample in accordance
with the particle size, a sensor and a signal processing unit, and the
measuring
device is arranged to process the sample as at least two fractions according
to
the particle size, the sensor is arranged to measure at least one fraction,
the
signal processing unit is arranged to receive a measuring signal from the sen-
sor and determine at least one parameter of at least one added substance in
at least one fraction measured.
[0012] The invention still further relates to a measuring device for
measuring recycled fibre pulp in a recycled fibre process, in whose manufac-
ture at least one of the following was used: paper, paperboard, pasteboard,
ink
having been transferred to the surface of the paper, paperboard, pasteboard.
The measuring device comprises a fractionating pipe arranged to receive a
sample from the recycled fibre pulp of the recycled fibre process and to ar-
range the particles of the flowing sample in accordance with the particle
size, a
sensor and a signal processing unit, and the measuring device is arranged to
process the sample as at least two fractions according to the particle size,
the
sensor is arranged to measure at least one fraction, the signal processing
unit
is arranged to receive a measuring signal from the sensor and determine at
least one parameter of the ink in at least one fraction measured.
[0013] Preferred embodiments of the invention are described in the
dependent claims.
[0014] The method and measuring device of the invention bring
forth a plurality of advantages. The measurement is independent of the wire,
the manufacturing geometry of the wire and the change in the manufacturing
geometry of the wire with time. The results of one measurement may be
adapted to measurements made on different wires. The reproducibility of the
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solution is good and the measuring circumstances manageable.
LIST OF FIGURES
[0015] In the following, the invention will be described in more detail
in connection with preferred embodiments with reference to the accompanying
drawings, in which
Figure 1 shows a recycled fibre process,
Figure 2 shows a fractionator,
Figure 3 shows an optical measurement,
Figure 4 shows different fraction distributions, and
Figure 5 shows a method flow diagram.
DESCRIPTION OF EMBODIMENTS
[0016] Let us first generally study a recycled fibre process by means
of Figure 1. First, raw material obtained from recycling, such as newspapers,
leaflets or magazines, may be fed into a pulping subprocess 100, the raw ma-
terial being mixed in a pulper comprised by said process with water such that
the consistency of the recycled fibre pulp becomes for instance 5 to 18% de-
pending on the pulping method used. The purpose of the pulping subprocess
is to chemically and mechanically disintegrate the raw material into recycled
fibre pulp, wherein the fibres and added substances, such as ink, are broken
down and separated into separate particles.
[0017] The pulper may be a rotating pulper, for example, wherein
the recycled fibre pulp rises up along with the wall of the cylindrical pulper
and
falls down by the action of gravity. During processing, the recycled fibre
pulp is
disintegrated into increasingly smaller parts and, finally, into fibres. The
falling
height of the recycled fibre pulp depends on the speed of rotation of the
drum.
The pulp may rotate in the pulper 20 to 40 minutes and, having passed the
pulper, enters the sieve section of the pulping subprocess, wherein it is
diluted
to a level of 3.5%, for example. This means that the largest impurities and
non-
degradable objects, such as staples, bits of plastic, etc., may be separated
from the recycled fibre pulp by means of openings (diameter e.g. about 1 cm)
in the sieve section. The objects separated from the recycled fibre pulp end
up
in a refuse conveyor.
[0018] A plurality of chemicals may be fed into the pulping subproc-
ess for separating the particles from each other. Sodium hydroxide is used to
raise the alkalinity of recycled fibre pulp to the level pH 9 to 10, for
example.
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Sodium hydroxide serves to swell the fibres and facilitate the detachment of
printing ink, for example. Soluble silicate, i.e. sodium silicate, in turn,
also im-
proves the detachment of printing ink, for example, and prevents the reattach-
ment of ink. At the same time, it buffers the pH to the desired level.
Hydrogen
peroxide, typically used for bleaching pulp, prevents the pulp from yellowing
in
connection with pulping. Other chemicals may be used in addition.
[0019] Next, the recycled fibre pulp may be washed in a washing
subprocess 102. At this stage, the consistency of the recycled fibre pulp is
usually lowered to a level of about 1%, for example. In the washing, flotation
may be used, which removes small free particles from the recycled fibre pulp.
In the washing, particles of all sizes are removed, but the majority of
particles
removed are in the size order of about 10 pm to 100 pm. In addition, the recy-
cled fibre pulp may be filtered (filter opening e.g. 2 mm) for better removal
of
objects unsuitable for recycled fibre pulp.
[0020] A dispersing subprocess 104 serves to further chemically
and mechanically detach ink particles adhered to the fibres of the recycled fi-
bre pulp. For mechanical processing, the dispersing machine of the dispersing
subprocess comprises a stator and a rotating rotor, whose blades process the
pulp. When the pulp passes between the blades, its speed changes rapidly,
whereby the fibres are subjected to mechanical stress, which detaches ink
from the fibres. At the same time, the purpose is to detach sticky substances
from the fibres and to reduce the particle size of added substances, such as
ink particles.
[0021] Finally, the recycled fibre pulp may be washed once more in
a second washing subprocess 106. In this washing, too, flotation may be used,
which removes small free particles from the recycled fibre pulp.
[0022] Each subprocess 100 to 106 of the recycled fibre process
may be controlled with a controller 108, to which measurement results may be
fed from different points of the recycled fibre process. The controller 108
may
utilize the measurement data concerning the subprocesses when optimising
the operation of each subprocess separately or when optimising the coopera-
tion of the different subprocesses in order to achieve an optimally good end
product. The purpose of the recycled fibre process is to remove substances
that are harmful to the recycled fibre pulp. Often the focus is on removing
print-
ing ink. The fraction in which the ink particles of the recycled fibre pulp
are af-
fects the removal of ink and is indicative of the operation/success of the
deink-
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ing process. The size order of the free ink particles affects the degree to
which
free ink can be removed from the recycled fibre process.
[0023] A sample or samples may be taken at least before one sub-
process 100 to 106, during at least one subprocess 100 to 106 or after at
least
one subprocess 100 to 106.
[0024] All in all, the aim in processing recycled fibre pulp is to de-
tach the fibres of the recycled fibre pulp from each other, to detach sub-
stances, such as printing ink, wax, hydrophobic agents, plastic, metallization
etc., added by transfer to the surface of paper, paperboard or pasteboard
after
the actual manufacture, and to remove the added substances from the recy-
cled fibre pulp.
[0025] In the mechanical and chemical processing of the pulping
subprocess and the dispersing subprocess, the aim is to optimize the follow-
ing, among other things: how well the fibres are detached from each other, are
fibres breaking in the pulping, how well ink is detached from the fibre and
the
filling materials and the coating paste, and into how fine particles the ink
is
split. The mechanical processing means of the pulping subprocess include, for
example: speed of travel of the pulp in the drum, i.e. production speed, the
consistency of the pulp in the drum, and the speed of rotation of the drum.
The
chemical processing means of the pulping subprocess include, for example:
the pH of the pulp in the drum, based on the dosage of sodium hydroxide, for
example, the proportion of silicate dosage, and the consistency of the pulp
(amount of water).
[0026] In dispersing, the separation of fibres and ink can be affected
primarily mechanically, including, among others: speed of travel of pulp
passing through the dispersing subprocess, i.e. production speed, consistency
of pulp in the dispersing subprocess, temperature of pulp in the dispersing
subprocess, speed of rotation of rotor, and amount of power fed into rotor.
The
amount of power fed into the rotor is typically controlled by controlling the
a
between the rotor and the stator, through which the pulp has to be conveyed.
[0027] Many substances transferred to the surface also remain on
the surface of the paper, paperboard or pasteboard. These include printing
ink,
plastic or metal, for example. An example of the use of metal is aluminium-
coated paper. After being transferred to the surface, some substances may be
partly or entirely absorbed inside the paper. These may include wax, some
(printing) inks and hydrophobic substances (such as glue).
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[0028] The substance to be added may be transferred to the sur-
face of the paper, paperboard or pasteboard by printing, spraying, spreading
or brushing. In addition, an added substance may be transferred by various
evaporation methods. The transfer may also be performed by immersing the
paper, paperboard or pasteboard into the added substance, or the added sub-
stance may be glued or melted so that it sticks to the paper, paperboard or
pasteboard.
[0029] It is common to the transfer that the paper, paperboard or
pasteboard is finished per se, and a substance is transferred to its surface
to
one or both sides from outside the paper, paperboard or pasteboard often ac-
cording to the purpose of use. Thus, the paper, paperboard or pasteboard has
already left the paper machine and possibly also the paper mill. The finished
paper, paperboard or pasteboard can then be transferred to a process,
wherein the added substance is transferred to the surface of the paper, paper-
board or pasteboard. The finished paper, paperboard or pasteboard may be
transferred to a printing process, a conversion process etc. For example, if a
package containing liquid is to be made from paperboard, the finished paper-
board may be coated with plastic, and a container of the desired shape may be
formed from the plastic-coated paperboard, and the container may be closed
by gluing after filling. In addition, text and/or images may be printed onto
the
surface of the paperboard or plastic by means of ink. The paperboard con-
tainer of this example may contain three different added substances: plastic,
glue and ink.
[0030] Figure 2 shows an apparatus for performing fractionation and
operating like a chromatograph. A sample taken from the recycled fibre proc-
ess may be fed through a valve 202 to a pipe 204, wherein the pressure, flow
and temperature of water pushing the sample forwards may be adjusted by an
adjuster 200. The desired chemical, which may be colouring agent for facilitat-
ing or enabling the measurement of the added substance, for example, may
also be added to the sample through the valve 202. For example, the fibres
may be coloured dark with a hydrophobic colouring agent, whereby the wax in
the sample is not coloured and remains lighter.
[0031] The length of the pipe 204 performing the fractionation may
be up to dozens or hundreds of metres, and its diameter may be from a few
millimetres up to dozens of centimetres. The pipe 204 may be manufactured
from a polymer, such as plastic, metal or the like. When the sample, which is
a
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suspension, flows in the pipe 204, the solid particles of the sample are ar-
ranged in accordance with the particle size such that the larger particles are
accumulated in the front part of the sample, the smallest particles being accu-
mulated in the rear part of the sample. Thus, large particles flow more
rapidly
than small particles. The particles of the sample may be arranged in fractions
according to the particle size, each of them comprising particles between the
desired upper limit and lower limit.
[0032] The flowing sample may be imaged by means of at least one
camera 206 and a source 208 of optical radiation. Optical radiation means
electromagnetic radiation from ultraviolet (about 50 nm) to infrared (about
200
pm). The image or images may be transferred from the camera 206 to an im-
age-processing unit 210, wherein the image or images generated may be
transferred to a display 212. The image-processing unit 210 comprises a proc-
essor, memory and one or more computer programs required for performing
image processing. The image or images may be transferred to the display 212
also directly from the camera 206 without processing performed in the image-
processing unit 210. Each image may a fixed image or a video image. Each
fixed image may present one fraction or an image presenting one fraction may
be generated or selected from the group of images. The video image, in turn,
may be a sequence of fixed images presenting shots from the front end of the
sample to the rear end of the sample. In this case, when progressing from the
first image (an image of the largest particles at the front end of the sample)
image-by-image forwards, the average size of particles diminishes. In
addition,
the consistency of the fractions may be measured optically by utilizing the at-
tenuation of optical radiation and, optionally, also the change in
polarization.
[0033] Fractions may be taken from the samples into sample ves-
sels 214 to 220, which may total N, wherein N is a positive integer and N is
equal to or more than 2. Each fraction in a sample vessel 214 to 220 may be
measured in a laboratory or the fractions may be measured as a sample flow-
ing in the fractionating pipe 204 by using one or more optical measuring meth-
ods.
[0034] The measuring device may further comprise a cake forma-
tion unit 222 for converting the fractions in the vessels 214 to 220 into
cakes
224. The cake unit 222 may comprise a container with a wire at the bottom and
a drying device, such as a suction unit, and a furnace for drying the fraction
filtered with the wire into solid substance.
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[0035] Measurements descriptive of the characteristics of fibres in-
clude for instance measurement of the length of fibre, measurement of the
length distribution of the fibres, measurement of the number of fibre bundles,
and brightness measurement. Of these, brightness measurement may also
measure ink characteristics (ink is adhered to the fibres).
[0036] Optical measurements of the characteristics of fibres may be
performed by spectroscopy or by means of image analysis, and the measure-
ments may be directed to a flowing sample or cakes made from sample frac-
tions. The optical measurements may be measurements of absorption, reflec-
tivity or scattering, wherein the polarization of optical radiation may be
utilized.
[0037] The size of a particle, such as the length of a fibre or the di-
ameter of an ink particle may be measured by using a line or matrix camera.
The measurement may concern the number, portion, size or size distribution of
free ink particles and to the number, portion, size or size distribution of
ink par-
ticles adhered to fibres.
[0038] Measurement of the total ink in the pulp, i.e. the effective ink,
may be performed by using measurement of optical radiation, which is the
ERIC (Effective Residual Ink Concentration) method, for example. In this case,
optical radiation on the desired band is directed to the pulp or cake, and re-
flected radiation is measured. Optical radiation may be infrared radiation,
whose band may be selected such that the absorption coefficient of the ink in
the pulp on the band used is higher than that of the fibres or other particles
in
the pulp. The band of infrared radiation may be between 700 nm and 1,500
nm, however, not being restricted thereto.
[0039] In addition, the amount or portion of ink adhered to the fibres
and the amount or portion of free ink detached from fibres may be measured
from the recycled fibre pulp. The measurement may be performed optically in
such a manner that an image is generated, from which the number, portion
and/or interrelationship of particles of different sizes and colours may be de-
termined by means of a suitable image-processing program. Such a solution is
described in US patent 6,010,593, which describes this measurement in more
detail.
[0040] Figure 3 shows the general principle of optical measuring
methods. Recycled fibre pulp 300 is directed to a transparent pipe 302 at the
wavelength used in the optical measurement. As the recycled fibre pulp pro-
ceeds in the pipe 302, the recycled fibre pulp is illuminated with optical
radia-
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tion generated by a source 304 of optical power. The optical power source 302
may be a led, a incandescent lamp, a gas discharge lamp, a laser or the like,
and the optical power source may illuminate the target in a pulse-like manner
or continuously. A camera 306, which may be a CCD camera (Charge Coupled
Device) or a CMOS camera (Complementary Metal Oxide Semiconductor), for
example, captures an image or images from the recycled fibre pulp 300 in the
pipe 302, either from the same side where the optical power source is located,
or from the opposite side. In addition, the camera 306 may be used to image
by using radiation scattered from the recycled fibre pulp. An image-processing
unit 308 may control the imaging and the illumination of the target and
perform
image processing and analysis. In the measurement of the length of fibres and
the size of ink particles, a capillary pipe having a diameter of from less
than
one millimetre to a couple of millimetres may be used as the pipe 302. In
other
measurements, the diameter of the pipe 302 may be larger, up to dozens of
centimetres.
[0041] Instead of the camera 306, a spectrometer may be used as
the sensor 206 for determining the spectrum of the optical radiation reflected
by each fraction. From the spectrum, the colour, brightness of the particles
etc.
and thus, the desired parameter to be measured, may be determined.
[0042] In contrast to what is shown in Figure 3, the source 304 may
direct a suitable energy to each fraction for achieving an acoustic response
signal in the particles of the sample. The source 304 may be for instance a
laser whose optical radiation causes acoustic oscillation of the particles.
Simi-
larly, instead of the camera 306, the sensor 206 may detect acoustic oscilla-
tion. Usually, acoustic oscillation is ultrasound. The frequency, amplitude
and/or phase of acoustic radiation depend on the characteristics of the parti-
cles, i.e. the parameter to be measured.
[0043] Figure 4 shows attenuation of optical radiation as a function
of the amount of water run in the fractionating pipe. Curve 400 shows meas-
urement before the washing subprocess of the recycled fibre process, curve
402 shows hyper-washing performed on a wire, and curve 404 shows the
measurement result after the washing subprocess of the recycled fibre proc-
ess. The vertical axis shows optically measured attenuation ATT and the hori-
zontal axis shows the amount L of water run in litres. The attenuation ATT may
be proportional to the consistency of the sample and thus, to the dry
substance
content in the different parts of the sample. The amount of water is inversely
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proportional to the size of the particles and it may be measured by initiating
the
measurement as the sample enters the fractionating pipe and measuring the
amount when the desired point or fraction of the sample is run to a measure-
ment point. The measurement point may be an area in the imaging sector of
the camera. The more water is run in the fractionating pipe, the longer be-
comes the distribution of the sample and the more accurately the particles of
different sizes are distinguished from each other. The length I of a sample
may
be assesses from the litre amount as follows:
1 = (M1 - MO)/A,
wherein M1 is the rear limit of the last fraction (in the example of Figure 4,
about 20 L = 20 dm3). MO is the start of the fractionation (in the example of
Figure 4 about 16 L = 16 dm3), and A is the cross-sectional area of the frac-
tionating pipe (in the example of Figure 4 about 0.08 dm) . Thus, the length
of
the fractionated sample in the example of Figure 4 becomes 200 dm = 20 m.
When the sample was taken, the sample was only about 25 cm long, and thus
the fractionating pipe has stretched the sample under the fractionation to
about
75-fold. If the sample flows about I m/s, the sample passes the optical meas-
urement in about 20 seconds. If the camera captures images at 20-ms inter-
vals, which corresponds to imaging at 2-mm intervals, 1,000 fixed images are
obtained from the sample, i.e. 1,000 imaged fractions, which, presented in
succession at the imaging speed, produce 20 s of video image. Only a few
fractions are required, for instance four (FR1 to FR4), whereby each result
measured from the fractions may correspond to the average of at most 250
images of the particles in the sample. Similarly, each fraction may be
displayed
with one representative image without averaging. In any case, the limits and
amounts of fractions may be selected freely from the images captured.
[0044] A manner of dividing fractions is presented in Figure 4 and
this example utilizes four fractions. Fraction FR1 of the largest particles
com-
prises particles in a litre amount of between 15.6 L to 16.3 L (in the order
of 5
mm to 2 mm, for example), fraction FR2 of the second largest particles com-
prises particles in a litre amount of between 16.3 L and 17.5 L (in the order
of 2
mm to 0.5 mm, for example), fraction FR3 of the second smallest particles
comprises particles in a litre amount of between 17.5 L to 18.3 L (in the
order
of 0.5 mm to 0.1 mm, for example), and fraction FR4 of the smallest particles
comprises particles in a litre amount of between 18.3 L and 20.4 L (in the
order
of 0.1 mm to 0.005 mm, for example).
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[0045] In the case of Figure 4, fraction FRI of curve 400 may com-
prise flakes, fraction FR2 may comprise long fibres, fraction FR3 may comprise
short fibres and FR4 may comprise ink particles, fine material and possible
other small material particles, of which ink particles are usually significant
as
regards the reuse of recycled fibre pulp. The ink particles of fraction FR4
are in
the order of 10pm to 100 pm, which is usually largely removed in the washing
subprocess of the recycled fibre process or which should be removed (almost)
entirely in hyper-washing. This kind of result can be seen from curve 402,
which presents the result of a hyper-wash performed on a wire. Since no parti-
cles are left in fraction FR4 in a complete hyper-wash, fraction FR4 of curve
400 may be given zeroes as predetermined values in the image-processing
unit and thus consider the distribution thus obtained as reference for the
wash-
ing to be prepared in the recycled fibre process. If the different fractions
of the
sample are collected into containers 214 to 220, as Figure 2 shows, the con-
tents of containers 214 to 218 may be combined (in this case, the fraction of
container 220 is filtered off from the sample), whereby also a concrete refer-
ence is obtained from the hyper-washed sample. The measurement result 404
of the sample taken from the washing subprocess 102 (or 106) of the recycled
fibre process may be compared with the reference, which is according to the
distribution 400 in fractions FRI to FR3 and has a constant value of 0 in frac-
tion FR4. The comparison may be performed by means of correlation, for ex-
ample. If the difference between the reference and the measurement result
404 is larger than a predetermined threshold value, the recycled fibre process
does not operate adequately well, and the quality of the end product does not
fulfil the desired quality requirements. In this case, the operation of the
recy-
cled fibre process has to be enhanced. If the difference is smaller than the
threshold value, the operation of the recycled fibre process can be considered
optimized and the quality of the end product sufficiently good.
[0046] Generally, any real subprocess of the recycled fibre process
can be compared with a corresponding reference. In this case, the measure-
ment of at least one parameter of at least one added substance may be per-
formed by determining the difference between the distribution of at least one
fraction measured after the desired subprocess and a predetermined distribu-
tion. The predetermined distribution thus depicts the desired distribution
after
the desired subprocess of the recycled fibre process.
[0047] The sample may be processed as at least two fractions by
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imaging the different particle sizes of the sample flowing in the
fractionating
pipe 204 with the camera 206, and generating at least one image representing
at least one fraction with the image-processing unit 210 from the images gen-
erated by the camera 206. Alternatively or in addition, at least two fractions
may be generated from the sample flowing in the fractionating pipe 204 into
the containers 214 to 220 and image at least one fraction in one of the con-
tainers 214 to 220 with the camera 206. Furthermore, alternatively or in addi-
tion, a cake 222 may be generated from at least one fraction and image the at
least one cake generated from the fraction with the camera 206.
[0048] The parameter to be measured may represent the portion in
the sample of at least one added substance attached to the fibres. The pa-
rameter to be measured may also represent the portion in the sample of at
least one added substance detached from the fibres. In addition, both above-
mentioned parameters may be measured.
[0049] Figure 5 shows a flow diagram of the method. In step 500, a
sample is taken from the recycled fibre pulp of the recycled fibre process
into a
fractionating pipe. In step 502, the particles of the flowing sample are
arranged
in accordance with particle size in the fractionating pipe. In step 504, the
sam-
ple is processed as at least two fractions according to the particle size. In
step
506, at least one parameter of at least one added substance of at least one
fraction is measured.
[0050] Although the invention is described herein with reference to
the examples in accordance with the accompanying drawings, it will be appre-
ciated that the invention is not to be so limited, but may be modified in a
variety
of ways within the scope of the appended claims.
