Note: Descriptions are shown in the official language in which they were submitted.
12075S4
The present invention re~ates to a method
and apparatus for determining the properties of
cellulose pulp, and mGre particularly for determining
cellulo~e pulp properties where informatlon concerning
the amount Gf pulp-sample analyzed is necessary in the
evaluation oE the pulp-property in question. By
cellulose pulp is meant here, and in the following~ both
pulps which contain more-or-less no lignin, and pulps
which have a high lignin content. Examples of such pulps
include chemical pulp, semi-chemical pulp, thermo-
mechanical pulp and mechanical pulp.
Background Art
When determining, for example, the lignin
content of pulps, a pulp-sample is taken and usually
reacted with a 0.1 N potassium permanganate solution.
The amount of potassium permanganate in numher of
millilitres of 0.1 N potassium permanganate solution
consumed for each gram of bone-dry pulp constitutes a
measurement of the lignin-content of the pulp. This
numerical value is generally called the kappa-number.
In Scandinavia it is routine procedure to use a
specified measuring method for determining the kapEa-
number, known as SCAN-C 1:77.
Correct determination of the amount of samp~e
analyzed is a primary general requirement of the SCAN-
method. The amount of pulp concerned is determineo by
weighing, and in order to know the weight of the dry
pulp, the pulp being weighed must be absolutely dry, or
the dry-solids content of the pulp being weighed must
be known. When the sample is -taken, the dry-solids
content is low, i.e. the sample contains much more water
than pulp fibres. According to the SCAN-method, if the
suspension is a screened-pulp suspension it is necessar~
to produce a pulp cake (3-4 grams) by filtering the pulp
through a Buchner funnel. The pulp is then air-dried in
a certain manner, and shredded into small pieces, ~nere-
after the sample is weighed and the analysis can commence
kh/~
~ .~)
~Z0~554
Aix-dryin~ of the pulp is normally effected b~ storing
the pulp sample in a drying cabinet at a ternperature
of 40C. Drying takes several hours, and in research
laboratories it is normal for the sample to be kept
in the cabinet from one day to the next, i.e. o~ernight.
When pulp is dried in this way, the dry-solids content
reaches a state of equilibrium lying at about 95~.
In operational laboratories, i.e laboratories
which are directly connected with the pulp-manufacturing
mill, the dryin~ time is shortened by first forming a
sheet from the pulp sample, and then drying the sample
in a drying cabinet at 105~C to absolute dryness, before
the sample is weighed. The drying times re~uîred ~ary
between different pulp samples, but normally lie within
the range of 45-60 minutes. The shortening o~ the dryin~
time by raising the temperature involves certain risks,
irt.e_-a'ia because _he pulp sample can c~a~ge chemically
as a result thereof, and consequently may not correspond
exactly to the pulp being produced.
Other methods for determining the lignin
content than those based on the consumption of potassium
permanganate are known. One such method is described in
Swedish Patent Application Number 80 00434-~, published
July 18, 1981, according to which the lignin content is
determined by measuring the increase in temperature which
results when chlorinating a pulp sample of well defined
dry-solids content. The pulp sample is de-watered by
pressing the same while simultaneously blowing t~ere-
through a gas which is weakly acti~e with respect to
oxidation, whereafter the maximum temperature increase is
recorded by blowing chlorine gas through the sample.
Although, when practicing this method, it would not seem
necessary to determine the amount of sample being analyzed,
particular attention must be paid to the dry-solids content.
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kh/~ ~
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:12075S4
Description of the Invention
Technical Problem
When determining, for example, the lignin
content of pulp, the step which includes determining
the amount of sample taken, i.e. the drying and weighing
of the sample, is extremely time-consuming, and is in
fact in the order of hours. Such a long lapse from the
time at which the sample was taken to the time at which
the result of the analysis is established constitutes an
obstacle in the correct control of the pulp-manufacturing
process. It is desirable to decrease the time-lapse
between taking the sample and establishing the result of
the analysis, without reducing the accuracy of the analysis.
This time-consuming quantity-determining step also
presents a serious problem in the determination of other
pulp properties, such as the measurement of washing losses
for example.
Solution
The aforedescribed problems are solved by means
of the present invention, which relates to a method for
determining at least one property including lignin
content of cellulose pulp fibers, which comprises
selectins a sample of cellulose pulp to be analyzed,
analyzin~ the pulp sample for the property, and determining
the cellulose pulp fiber content of the pulp sample by
subjecting the analyzed sample in the form of a cellulose
pulp fiber suspension of low consistency to an optical
measurement capable of measuring fiber content, thereby
determining the property.
A prime feature of the present invention is that
the quantitative measurement of the pulp is not carried
out until the actual analysis of the pulp property has
been made, and that the measurement is effected optically.
On the other hand, if the reverse procedure is taken, so
that the quantitative measurement is made before the
analysis no reproduceable result can be obtained.
- 3 -
1207S5~
The present invention also relates to apparatus
for determining at least one property including lignin
content of cellulose pulp fibers, comprising means for
selecting a sample o~ cellulose pulp to be analyzed,
means for analyzing the pulp sample for the property, and
optical measuring means capable of measuring fiber content
for determining the cellulose pulp fiber content of the
pulp sample, means being arranged in a sequence for first
analyzing the pulp sample, and then determining the cellulose
pulp fiber content by the optical measuring means, thereby
determinin~ the property.
The location in the pulp-manufacturing process at
which a sample is taken is partially dependent upon the
pulp property of interest. ~n important property of the
pulp is its lignin content. The lignin content is of '~
interest during several stages of the pulp-manu~acturing
process. Normally a pulp sample is taken for determining
the lignin content of the~pulp after the cooking stage
and after one or more bleaching stages (for example
oxygen-gas bleaching stage and chlorination stage) and
after extraction stages.
The pulp concentration of the removed sample varies
with the location at which the sample was taken. In order
for the optical quantitative measurement to be made with
great accuracy, the sample shall be present in the form
of a fibre suspension having a concentration below 5%,
preferably below 1%. The invention is suitable for both
laboratory purposes and for operational purposes, i.e. in
direct connection with the pulp-manufacturing process,
and may be automatized. Treatment of
:~`
~2~)7554
thc pulp sample subsequent to being taken ~rom the pulp-manu-
facturing process is depcndcnt upon whether the invention is
applied for laboratory purposes or is applied in direct connec-
tion with the pulp manufacture. IYhen determining the lignin
content of the pulp, the sample must be freed from waste liquor,
and is therefore washed with water. I~hen taking a pulp sample
after the digester for example, it is suitable to screen the
sample. This is not necessary, however, when, for example, a
sample is taken after an oxygen-gas bleaching stage. If the
l~ pulp sample is taken just prior to the stream of pulp suspension
entering a washing filter, the concentration is normally about
~ ~en determining the lignin content during operation, it is
suitable to maintain approximately the same pulp concentration
while washing and optionally screening the pulp sample, which
lS means that the sample arrives at a sample-determining reaction
vessel in the form of a fibre suspension having a concentration
of about ~. It is fully possible, however, to increase or
decrease the fibre concentration temporarily, while washing
andJor screening the sample. It is also possible to remove the
sample at a much hi~her concentration and to introduce the
sample :;nto the reaction vessel at said higher concentration,
or to thin the sample with water during its passage to said
vessel. It is also possible to take the sample at a concentration
of about 1% and then to increase the concentration by withdrawing
liquid from said sample, and pass the sample to the reaction
vessel. When applying the invention for laboratory purposes,
the following procedural steps are taken for example. If the
pulp sample is taken, for example, from the blow-line of the
digester, the sample is screened in a so-called Wennbergs screen.
After screening the sample, the pulp is further washed in a
sheet mould and formed into a sheet, which is couched with a
dry blotting sheet, so as to increase the concentration to
about 30~. An approximate amount is then taken from the resul-
tant sample sheet, this approximate amount being about three
times the calculated dry sample. In practice this is effected
by the person making the analysis tearing off a certain portion
of the sample, which in size is approximately the same from time
to time. Since the amount of pulp is not critical, it is
` ~ ~2~7~54`
easy to establis]l ;I routinc l~itll rcsl~cct to the torn-o~f
pulp-sample pieccs. The sample pieces are then dropped into
the reaction vessel.
If determination of the ]ignin content is effected in
accordance with the method based on the amount of 0.1 N
potassium permanganate solution consumed by the pulp in milli-
litre per gram of bone-dry pulp, as in the SCAN-method for
example, Appendix B, the following applies. When taking a
laboratory sampl-e ln accordance with the invention, the pulp is
introduced into the reaction vessel in solid form with an
estimated bone-dry weight of about 1 gram. The sample is sus-
pended in 400 ml of water. When sample taking is automatized
in accordance with the~inven~ion, the pulp sample arrives at
the reaction vessel preferably in the form of a suspension.
Thus, the reaction vessel should be able to accommodate much
more than 400 ml. According to a preferred embodiment of the
invention, the pulp suspension is introduced to the reaction
vessel in a volumetric excess, the reaction vessel being pro-
vided, for example, with a closeable spillway located at a
level corresponding to a volume of 400 ml. Liquid, with or
without fibres, is drained off through said spillway, until
the sample volume of 400 ml is obtained. As will be understood,
it is also possible to supply the pulp sample in the form of a
- suspension in a volume beneath 400 ml, and then to supply water
up to 400 ml or a~ove. In this latter`case, the surplus liquid,
with or without fibres, must be tapped off before commencing the
actual analysis. Naturally, the sample can be suspended in a
volume which deviates from 4~0 ml, i.e. the volume may be both
greater and smaller than 400 ml.
As will be understood from the aforegoing, when practicing
the method according to the invention it is no~ necessary to keep
a check on the whole of the amount of fibre which the sample
comprises at the time of taking the sample. On the other hand,
it is absolutely necessary to keep a check on all fibres while
carrying out the analysis and subsequent to the completion of
the analysis for the quantitati~e determination.
,,"
~l207S5~
In the SCAN-method, the sample, i.e. pulp of appro~imately
1 gram bone-dry weight suspended in 400 ml of water is admixed
with 50 ml 4 N-sulphuric acid for acidification. 50 ml of 0.1 N
potassium permanganate solution is then added. The reaction is
interrupted after 10 minutes by adding 20 ml of 1 N potassium
iodide solution, whereafter the iodine formed is titrated with
0.~ N sodium thiosulphate solution. Starch is used as an indicator.
Thus, the chemical analysis means that the pulp suspension is
furhter diluted. According to a preferred embodiment of the
invention, all of the pulp suspension is charged to a collecting
vessel. Despite the dilution of the sample effecte~ by adding
the chemical solutions, the sample i~s preferably further diluted
with a measured amount of water. This is utilized at the same
time for rinsing the reaction vessel, so as to ensure that all
pulp is transferred from the reaction vessel to the subsequent
optical measurement of the fibre content. The collecting vessel
has two functions, firstly one of collecting the pulp suspension
and seco~dly one of enabling air to be evacuated from the pulp
suspension when air has been mixed therein. The pulp suspension
is circulated from the collecting vessel to the optical measuring
means, and then back to the collecting vessel, by means of a
circulation line and a pump. A collecting vessel is not always
necessary, however, since the pulp suspension can be passed
directly from the reaction and measuring vessel to the optical
measuring means. It is also possible for one and the same vessel
to function as a reaction vessel, measuring vessel and collecting
or air-ventilating vessel.
The optical measuring means may be any kind of measuring
means having suffisient accuracy and reliability for the purpose
intended. One example Df a suitable optical measuring means is
~ fr~?Je r~
the TP21Laboratory Fibre Analyzer sold by the ComPany Eur-Control.
In this measuring device, the fibre suspension passes a trans-
parent tube. Arranged on one side of the tube is a light souTce
which sends a light beam through the tube and the fibre suspen-
sion, via a lens. A detector is arranged on the opposite side ofthe tube, on level with the transmitted light beam. A further
detector is arranged within an angle of 10 degrees from the
,: ' - I
1~Z07S54
.
firstmentioned detector. By measuring the amount of light which
passes straight through the sample and the amount of light which
deviates 10 degrees from said direction, information is obtained
concerning the amount of fibre in the ibre suspension. For
s example, it can be read-off as mg fibres per litre suspension
liquid. The number of milligrams is obtained by comparing the
light intensity measured at the sampling moment with previously
made calibration tests. It has been found that when using said
device, a particularly suitable fibre content in the pulp suspen-
lG sion is 0.4-0.8 g, i.e. 400-800 mg, per litre.It is also possible,
however, to measure both lower and higher fibre contents.
Since the optical measuring means gives the fibre content
of the suspension in mg/l, and since exact data is found con-
cerning the amount of liquid supplied from the time the pulp is
introduced into the reaction vessel, it is possible, by applying
simple mathematics, to calculate the amount of analyzed pulp in
grams, without weighing the pulp at all.
Other types of optical concentration-measuring devices
are also found on the( ma~ket )For example, one such measuring -
2 ~ device, designated ACM/ is sold by the company Cerlic Electronics
AB. The measuring principle of this device is based on the ability
of the cellulose fibres to absorb and reflect light. In this
respect, the loss of light between transmitter and receiver
provides a measurement of the fibre concentration. The light
used is infra-red, transmitted in pulse form. According to
information, the measuring range lies within a concentration
range of 0.00005 to about 4~.
The present invention can also be used for measuring
other pulp properties, such as the washing losses during pulp
manufacture for example. In this analysis, pulp samples are
taken and thinned or diluted with water to a given ~olume~ The il
amount of washing losses, i.e. the undesirable organic and in-
organic conten~ of the pulp after cooking and washing, can be
deteTmined by means, for example, of ion-selective electrodes.
The pulp suspension is then passed to an optical measuring means, I
where the fibre content is determined, for example, in mg~l. i
I
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~207~i54
Since the sample has been diluted with ~ater to a g;vcn ~olume,
it is a simple matter to calculate the washing losses and to
state said losses in, for example, kg Na2SO4 per ton of pulp.
The washing losses can also be determined by passing a small,
S representative portion of the sample liquid to a flash photo-
meter, and analyzing said liquid therein. In this case, the
amount of sample taken must be measured and subtracted from
the given volume when determining the fibre content.
Advant~
When determining the lignin content of cellulose pulp
in the form of kappa numbers, in accordance with the methodology
applied hitherto for example, the time taken to dry the pulp
sample prior to weighing the same is of the order of hours.
When drying the sample at a temperature of 105C in accordance
with the so-called quick kappa number method, the time taken to
dry the pulp sample is from 45-60 minutes, to which must be
added some minutes for weighing the sample. This time-consuming
drying operation, and also the weighing operation, are elimina-
ted when the amount of cellulose pulp sampled is determined in
accordance with the invention. The optical quantitative deter-
mination according to the invention, which is carried out on a
sample which has already been analyzed, is completed in approxi-
mately 4-5 minutes, which means that the invention enables a
reliable value to be obtained with respect, for example, to
the lignin content of a pulp sample at least 40 minutes quicker
than has previously been possible when applying analysis techniques
established within the cellulose pulp industry. This is of great
significance in controlling the pulp-manufacturin~ process. Many
advantages are achieved by the elimination of the necessity
to weigh the pulp, this necessity at times being troublesome.
~hen the pulp sample is dried at 105C to absolute dryness in
accordance with earlier techniques, ~he pulp is not in equilib-
rium moisture-wise with the ambient air dùring the weighing
opera~ioD, and hence the persGn weighing the sample must be
extremely quick in order for a correct weighing result to be
.
~07554
obtained. If part of the pulp sample is lost during passage of
- the sample between the weighing station and the analyzing station
it is disastrous to the result of the analysis. In the process
of the invention, however, any loss of pulp fibres between the
S sampling moment and ~he moment of analysis is without influence
on the result of the analysis. In order to shorten the sample-
treatment time, i.e. the time taken in drying and weighing the
sample, it has been suggested that the pulp sample taken is
divided into two parts, whereupon the dry-goods content is
determined on one sample part and the analysis is made on the
other sample part, which is weighed with a relatively high water
content, whereafter the bone-dry weight is calculated subsequently.
In order for such a method to function correctly, however, the
division of the sample into ~wo parts must be done in such a
manner that both the dry content and the other properties
coincide between the samples. This is extremely difficult to
- achieve in practice. On the other hand, when practicing the
method according to the invention it is those fibres which have
already been the subject of analysis (or a given percentage
thereof) which are subjected to quantitative determination.
Brief Description of the Drawings
In Figure 1 there is illustrated a first apparatus array
for use when practicing the invention for laboratory purposes.
Figure 2 illustrates a second apparatus array, for use
when practicing the invention for laboratory purposes.
Figure 3 illustrates an apparatus array for use when
applying the invention in direct connection with a pulp-manu-
facturing process.
Figure 4 is a flow sheet illustrating handling of the
pulp sample from the sampling location, over the chemical ana-
lysis stage to the quantitative determinii~g stage in an
automatized embodiment of the invention.
Figure 5 illustrates a comparison made between the
lignin content of pulps (kappa number) obtained in accordance
3~ w;th the SCAN~method and in accordance with the invention.
~ - I
~.æo7~s~
Prcferred Embodiment
Application of the invention when determining the
kappa-number of cellulose pulp will now be described with
reference to Figures 1 - 4.
The array of apparatus illustrated in Figure 1 is suitable
for use in laboratories, for example research laboratories and
works laboratories. An estimated amount of pulp, approximately
3 g, having a concentration of about 30 ~ is introduced into
the reaction vessel 1. The pulp sample has not been weighed but
the laboratory assistant introduces into the vessel an amount
which he judges to weigh about 3 g. 400 ml of wa~er are then
added to the reaction vessel ? whereafter the pulp sample is
slurried to form a suspension, by means of a propeller agitator 2.
A 0.1 N solution of potassium permanganate (KMnO4) is stored in
vessel 3, while a 0.2 N solution of sodium thiosulphate (Na2S2O3)
is stored in vessel 4. The pulp suspension is acidified with
50 ml of 4 N sulphuric acid ~H2SO4) measured and pipetted
manuallyj whereafter 50 ml of potassium permanganate solution
is supplied from vessel 3 via metering means 5, called dosimeter.
The pulp is allowed to react with the potassium permanganate
supplied for 10 minutes~ whereafter the reaction is interrupted
by supplying to the reaction vessel 1 20 ml of a 1 N solution of
potassium iodide (KJ~. The potassium iodide solution is measured
and added manually, by means of a so called vogel-pipette. Some
drops of starch solution are added as an indicator. Unconsumed
potassium permanganate reacts with the potassium iodide added to
form iodine (J2). Occurring free iodine is titrated with the
sodium thiosulphate solution in reaction vessel 1. The sodium
thiosulphate solution is passed from the vessel 4 to the reaction
vessel via the graduated metering means 6. The amount of sodium
thiosulphate solution added is noted at the end point, whereafter
an equivalent amount of iodine and potassium permanganate are
calculated. Since information is available with respect to the
amount of potassium permanganate added and the amount of un-
consumed potassium permanganate, there is obtained bv subtraction
the amount of potassium permanganate which has reacted with the
pulp .
I
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~20755~
12
The contcnts of ~he reaction vessel 1 are poured into
the measuring vessel 7. The reaction vessel is thorougly rinsed
with water, so that all fibres subject to analysis are trans-
ferred to the measuring vessel 7. This is graduated, and the
water is supplied to the pulp suspension thro~gh line 8, up to
a mark showing 2 litres. The resultant suspension is then trans-
ferred, via line 9, to the collecting and air-purging vessel 1~.
A stream of suspension is taken from the vessel 10 and moved in
a closed circuit by means of pump 11 and circulation line 12.
As the suspension circulates, it passes an optical measuring
means 13, which incorporates, inter alia, a transparent bulb,
a light source, detectors and a unit for registering and calcu-
lating measurement signals. The capacity of the pulp 11 is such
as to constantly maintain the fibres in the suspension in motion
and uniformly distributed therein. Since the sample comprises
approximately 1 g of bone-dry pulp and the pulp is suspended in
~ litres of water, the pulp concentration is approximately
500 mg/l. Subse~uent to the pulp suspension having passed the
optical measuring means 13 a repeated number of times, there is
obtained a signal which, with the aid of previously made callibra-
tion tests, provides information of the exact fibre content in
mg/l. Since the volume is known ~2 litres) the amount of pulp in
grams is readily obtained. The kappa-number of the pulp is
obtained by dividing the amount of potassium-permanganate
solution consumed in millilitres with the amount of pulp expressed
in grams. I~hen measurement of the fibre content of the pulp
suspension is completed, th~ suspension is passed to a drain,
through the line 14.
Figure 2 illustrates a simplified array of apparatus for
laboratory purposes, in which the Teaction vessel and the
measuring vessel are one and the same vessel. Sodium thiosulphate
solution is stored in the vessel 15 and passed to the measuring
and reaction vessel 17 through the metering means 16. The potassium
permanganate solution is stored in vessel 18 and is passed to
the reaction and measuring vessel 17 through the metering means
19. The pulp sample, which has an approximate bone-dry weight of
. .
.
.
~o~554
1 g, is charged to the vessel 17, whereafter 400 ml of ~.ater
are supplied to the vessel through the line 20. The pulp sample
is slurried by means of the propeller agitator 21 to form a
suspension, whereafter the chemical analysis is carried out in
the aforedescribed manner. Upon completion of the analysis,
further water is added through the line 20, so that the level
o liquid rises to the mark denoting 2 litres. The suspension
is then tapped-off through line 22 and passed to the collectlng
and air-purging vessel 23. The suspension is passed from this
vessel into a closed circuit for a repeated number of times,
through the line 24 and the vessel 23 by means of ~he pump 25.
During its passage around the closed circuit, the suspension
passes the optical measuring means 26, for measuring the fibre
content in mg/l. Subsequent to terminating the quantitative
determination, the suspension is passed to a drain, via the
line 27.
Figure 3 illustrates an apparatus array which is more
automatiz.ed than the arrays of apparatus illustrated ln Figures
1 and 2. The Figure 3 embodiment of the invention is primarily
intended for use in the mill, for example in the digester
house and/or the bleaching department.
In the centre of the array there is located a combined
measuring and reaction vessel 28~ The pulp sample is supplied to
the vessel 28 in the form of a suspension of low concentration,
through the line 29. The amount of suspension charged is not
critical, and may reach, for example, to 700-800 ml. Subsequent
to supplying : this amount of the suspension to the reaction
vessel 28, a valve on the line 30 is opened~ so as to drain the
suspension down to a level with the outlet of said line. This
will leave 400 ml of suspension in the vessel 2~. If desired,
the suspension can be agitated by means of the propeller agi-
tator 31. The sodium thiosulphate solution is stored in the
vessel 32, and is supplied to the reaction vessel through the
metering means 33. The potassium permanganate solution is s~ored
in the vessel 34 and is supplied to the reaction vessel via
the metering means 35. The sulphuric acid solution is stored
in the vessel 36 and is supplied to the rection vessel via
the metering means 37O The potassium iodide solution is stored
~ '
~207~iS4 - -
14
in the vessel 38 and is p~lssed to thc leaction ~csscl via thc
metering means 39. Subsequent to adding sulphuric acid and
potassium permanganate to the suspension, the lignin-containing
pulp is permitted to react with the potassium permanganate for
a given length of time. According to the SCAN-method a reaction
time of 10 minutes shall be employed. The reaction time, however,
can be reduced to, for example, 5 minutes. The reaction is
interrupted by introducing potassium iodide. Sodium thiosulphate
is then added, for reaction with the iodine formed. Inserted
into the reaction vessel 28 is a pair of redox electrodes,
platinum-electrode 40 and reference-electrode 410 The redox-
electrode pair extend from the end point titrator 42, which is
connected to the means 33 for metering the sodium thiosulphate
solution. I~hen all iodine has been consumed by reaction with
lS sodium thiosulphate, a- jumping change in the redox potential
takes place, whereupon the supply of sodium thiosulphate solution
is terminated and the amount added can be read-off from the
metering means 33. Subsequent to finalizing the chemical analysis,
it remains to determine the amount of pulp sample used.
In order to bring the pulp suspension to a concentration
suitable for the optical measuring operation, the suspension is
further diluted by adding water through the line 43. The water is
supplied so that the level of liquid rises to, for example, the
two litre mark on the graduated reaction vessel 28. The suspen-
sion is passed to the collecting and air-purging vessel 45
through the line 44. The suspension is caused to circulate
through the line 47 and the collecting vessel 45 in a closed
circuit~ by means of pump 46. During its passage around the
circuit, the flow of suspension repeatedly passes the optical
measuring means 48. With respect to the thinning or dilution
of the suspension in the reaction vessel 28 with water, it is
not necessary to thin the suspension to th~ intended volume in
one stage~ preferably the suspension is thinned in a first stage
to a given volume and then passed to the collecting vessel 45.
A further measured amount of water is then supplied through
the line 43, this fur~her quantity of water functioning at the
same time as a rinsing liquid, for the purpose of removing all
pulp fibres from the reaction vessel Z8. I~Then the quantitative
determination has been made, the pulp suspension is passed to a
drain through the line 49.
, _ , ,
1207S5~
In the apparatus array in which tlle method according to
the invention is carried out, it is not necessary to take any
manual measures, since determination of the lignin content of
the pulp takes place purely automatically. It is possible,
5 however, to take some manual steps even with this embodiment
of the invention. For example, the situation can arise in
practice that someperson in the digester house or bleaching
department may wish to determine the kappa number of pulp taken
from a continuous web and at a location where the pulp is not
present in the form of a suspension. In such a case, the pulp
sample is released in solid form and passed by hand down into
the reaction vessel 28, whereupon water is supplied through
the line 43 up to a level with the outlet for line 30, i.e.
to a volume of 400 ml. In this case it is necessary to use
the propeller agitator 31, to release the pulp fibres in the
water to form a suspension suitable for chemical analysis.
Figure 4 is a flow sheet illustrating a fully automatized
embodiment of the invention. The Figure illustrates the path
moved by the pu~lp sample from the extraction location directly
in a pulp-transport line via washing and optional screening,
chemical analysis, optical quantitative determination, to its
discharge through the drain. The Figure also illustrates collec-
tion of data and the use of computer for calculating the kappa
number.
The line 50 is arranged to convey, for example, unbleached
pulp in the form of a suspension. Connected to the line 50 is a
sample taXing device 51. A number of sampling devices are found
on the market, and any one of these can be chosen. The sample
volume is dependent upon the pulp concentration in line 50. The
volume is adapted so that the bone-dry weight of the pulp intro-
duced into the reaction vessel 52 is about 1 g. The sample taken
is passed through the line 53 to a vessel 54, in which the pulp
is washed and optionally screened. Clean water is passed to the
vessel through the line 55, and water containing washed-out and
optionally screened impurities leaves the vessel through the
line 56. The sample volume can be readily corrected in this
stage if so desired. The washing and optional screening in
,
~207S5~ -
16
~ssel 54 nlust be carlied out accurately, so tl~t no washin~
losses (organic and inorganic compounds) accompany the pulp
sample into the reaction vessel 52. The washed and optionally
screened sample is passed to the reaction vessel 52 through
the line 57. Sulphuric acid is passed from the storage and
metering vessel 58 to the reaction vessel 52, through the line
59. Corresponding means for potassium iodide are referenced 60
and 61, while corresponding means for potassium permanganate
are referenced 62 and 63 and for sodium thiosulphate 64 and 65.
An end point titrator 66 provided with a pair of electrodes is
arranged in the reaction vessel 52 in order to detect when all
iodine has been consumed by the sodium thiosulphate supplied.
The function of the end point titrator can also be incorporated
in a computer. Upon conclusion of the chemical analysis J water
is passed through the line 67 to the volumetrically graduated
reaction vessel 52. The pulp suspension is then passed through
the line 68 to the optical quantitative determining means 69.
Subsequent to determining the fibre content, for example in
mg/l, the pulp suspension is passed to the drain means, through
the line-70.
The whole handling of the pulp sample from the extraction
location to its discharge to the drain means, and all peripheral
equipment for establishing the lignin content of the sample
taken expressed in kappa number, are controlled ~otally from a
control unit 71, which includes a computer. The broken lines
illustrate that the various devices are connected to the control
unit 71. All steps from the step at which a signal is trans-
mitted to the effect that a sample of the pulp shall be taken
to the step where a signal is sent to the effect that the sample
upon which an analysis has been concluded shall be sent to the
drain means are controlled by means o the computer. When
applying the invention in analyzing the lignin content of the
pulp it is not possible to follow the same continuously, but
that the lignin content mus* be determined intermittently. In
comparison with previously known analysis ~echniques based on
the supply of chemicals in aqueous solutions and titrimetry, ~hen
practicing the present invention, however, the total time taken
from the time at which the sample is extracted to the time at
which infor~ation is obtained concerning the kappa number is
considerably reduced.
. .
.,`, , '
~207~iS4
17
The time t~kcn in this rcspect i5 about 20 minutes. A
considerable part of this time, namely 10 minutes, is consumed
by the time which lapses from the moment at wllicll the potassium
permanganate is added to the time at which the reaction between
the pulp and the potassium permanganate is interrupted, by adding
potassium iodide. According to SCAN-standards this length of
time shall pass, although it is fully possible to reduce this
time to, for example, 5 minutes, which means that the total
circulation time is lowered to about 15 minutes. This considerably
improves the possibilities of controlling different steps in
the pulp-manufacturing process, since the affect of different
measures on the lignin content of the pulp will be brought to
the knowledge o~ the operator, if not instantaneously within a
comparatively short time and with a high degree of accuracy.
In order to further illustrate the method according to
the invention, there is given below a number of working examples
relating to laboratory tests carried out in accordance with
known techniques and in accordance with the present invention.
Example 1
Two pine pulp samples and two birch pulp samples were
taken from four locations in a sulphate pulp mill. The pine pulp
was taken in part directly after the digester and in part after
subjecting the pulp to an oxygen-gas bleaching process. The
birch pulp was taken in part after the screening department and
before the first bleaching stage, and in part after the first
extraction stage.
The kappa number of the pulp samples were determined in ~
part in accordance with known techniques and in part while
practicing the invention.
By known techniques is meant here a modified SCAN-method
(SCAN-C 1:77, Appendix B). The extrac~ed pulp samples were treated
in the following manner. The pine pulp taken directly after the
digester was screened in a so-called l~ennbergs screen. After
screening the pulp, the pulp was further washed in a sheet
mould and shaped to sheet form, which was couched with a dry
blotting sheet, so as to increase the concentration of the pulp
- -
1:~075~;~
to about 30 ~0. The sheets were then dried in a drying cabinet
to 105C, until they were absolutely dry. The time taken to dry
the sheets was 45-60 minutes. When the sheets had reached abso-
lute dryness, a suitable sample quantity, i.e. about 1 g, was
quickly weighed on analysis scales, to an accuracy of 0.001 g.
The pulp samples were then transferred to a titration vessel,
where the chemical analysis was carried out in accordance with
SCAN-standards. The remaining pulp samples were treated in a
similar manner, with the exception that screening was excluded.
The chemical analysis provided data of the amount of 0.1
potassium permanganate solution consumed in millilitre by the
different samples. By dividing these numerical values with
respective weights of the weighed samples, information was
obtained concerning the kappa number of the different samples.
15The following steps were taken when proceeding in
accordance with the present invention. The extracted samples
were washed and formed into sheets in the aforedescribed manner.
- In the case of-.the pine pulp samples taken directly after the
digester, these were also subjected to screening, similar to
the aforedescribed. From the wet sample sheets thus obtained
was taken an estimated amount, about 3 times dry sample. The
sample pieces were obtained by manually tearing the wet sample
sheets. Quite simply, the laboratory assistant tore from the
sample sheets pieces of approximately the same mutual size.
Since the amount of pulp was not critical, it was easy to
establish a routine with regard to ~he size of the sample
pieces.
The apparatus array illustrated in Figure 1 was used
when carrying out the tests accoIding to the invention. The
aforementioned sample pieces were placed in the reaction vessel
1 and the chemical analysis carried out completely in accordance
with SCAN-standards. With regard to the chemical analysis, full
conformity existed between the two test series. This means
that the ~pparatus identified in Figure 1 by references 1, 2,
3, 4, 5 and 6 were used in both series. In ~he test series
according to the inven~ion, the pulp samples were transferred
from the reaction vessel 1 to the measuring vessel 7. The pulp
~.2o7S54
19
.
samples comprised a suspension containing about 1 g pulp fibres,
400 ml initially supplied water, 50 ml sulphuric-acid solution,
50 ml potassium-permanganate solution, 20 ml potassium-iodide
solution, some drops of starch solution, and a given number of
ml sodium-thiosulphate solution varying with the lignin content
of the pulp sample supplied. Water was introduced into the
graduated measuring vessel 7, through line 8, up to the mark
indicating a volume of 2 litres. This means that the fibre
content of the suspension lay at around 500 mg/l. The fibre
suspension was tapped-off into the collecting and air-purging
vessel 10. The.fibre suspension was caused to circulate, by
means of a pump 11, from the vessel 10, through the pump and
through line 12, back to the vessel 10. While circulating, the
fibre suspension passed through an optical measuring means sold
by the company Eur-Control under the name TP2 Laboratory Fibre
Analy~er. The operational mode of this measuring means has been
earlier described. The measuring signals obtained were compared
with measuring~signals obtained in previous calibrat;ng tests,
thereby providing information concerning the fibre content in
mg/l. Information concerning the amount of analyzed sample in
grams was also obtained hereby. The kappa number of the pulp
samples was obtained by dividing the consumption of potassium
permanganate in millilitre with the amount of sample in gram.
The result achieved is shown in Figure S, where the
measuring results obtained is plotted in a dispersion diagram
with kappa number measured totally in accordance with the
SCAN-method on one axis and the kappa number measured while
applying the method according to the invention on the other
axis.
As previously mentioned, four different pulps were
analyzed in accordance with the two methods. The following
symbols were used.
= Pine pulp after digester
~= Pine pulp after oxygen-gas bleaching
3~ X = Birch pulp before first bleaching stage
E3= Birch pulp after first extraction stage
.. .
.
~207S54
Thc follo~ling procedure has been followed ~hen plot~ing
the measuring rcsults; if, for example, a given extracted pulp
sample had given a kappa number of 30 according to the SCAN-method
and 32 when applying the method according to the invention, an
imaginary line was drawn from the numerical value 30 on the y-axis
parallel with the x-axis and a further imaginary line was drawn
from the numerical ~alue 32 on the x-axis parallel with the y-
~ axis, and a dot was placéd where these imaginary lines inter-
sected one another. This means that if exactly the same numerical
values are obtained in both analyses methods, al~ points will
fall on a line which extends from the point of intersection `-
bétween the two axes and which has à slope of precisely 45C.
63 comparison tests were plotted on the diagram. It was found
by linear regression analysis ~carried out in the manner described
on pages 323 and 324 of the book "Statistical Package for the
Social Sciences", second edition published by McGraw-Hill Book
Company) of the measured pair values that the following relation-
ship preuails. be.tween the measured numerical values
!
Kappa numberscAN = 1-07- Kappa numberInventiOn . .
Dispersion of the separate dots around this line is
. very small, evident from the fact that the correlation coefficient
r (calculated in the manner described on pages 280 and 281 of
the book '7Statistical Package for the Social Sciences", second
edition published by McGraw-Hill Book Company) is 0.999. The
ideal value of r is.l.0, from which it can be seen that the
correlation achieved is surprisingly good.
. It will be seen ~rom the above formula that the kappa
number measured while applylng the invention is somewhat lower
than the kappa number measured totally in accordance with the
SCAN-methodO The reason.for this difference has not been estab-
lished, although it may be due.- to the different treatment
processes to which the pulp samples were subjected. In the
analysis made in accordance with the SCAN-method, the samples
were dried at high temperatures = 105C prior to the chemical
" . I
~207~54
analysis, while when carrying out the method according to the
invention the samples were not dried, and the pulp was intro-
duced into the reaction vessel at a pulp concentration of about
30 %. Similar differences have been observed when making compari-
sons between kappa numbers of pulps which had been dried attemperatures of 105C and at temperatures of 40C, both drying
procedures being in accordance with the SCAN-method. It would
appear from earlier tests made by us that relatively quick
drying of the pulp at high temperatures leads to a higher kappa
number compared to the case when the pulp is not dried at all
or is ,dried very leniently.
The aforeillustrated good correlation between kappa
number measured totally in accordance with the SCAN-method and
kappa number measured while applying the invention illustrates
that it is possible to decrease the total treatment time when
determining the kappa number of pulps, by at least 40 minutes
while maintaining a high degree of accuracy in the analysis.
Exempel 2
Sulphate pulp was taken directly after the digester.
The pulp was analyzed in part in accordance with the SCAN-method
tdrying the pulp for 45-60 minutes at a temperature of 105C~
and in part while applying the method according to the invention,
implying that the pulp was neither dried nor weighed prior to
the chemical analysis. The pulp sample taken was screened and
washed in the same manner as that described at the beginning
of Example ]. Ten analyses were made in accordance with respective
methods. The measuring results obtained are set forth in Table 1.
,-
~207S54
22
Table 1
Kappa number accordingKappa number according
to the invention to the SCAN-method
31.5 32.9
31.3 33.2
31.6 33.5
31.4 33.4
31.0 33-5
31.4 33.5
30.8 - 33 7
31.6 33.6
31.2 33.5
31.3 33.3
Mean value 31.3 33.4
Disperson 0.26 0.23
The dispersion = S is calculated in the adopted manner, described,
for example, on page 184 of the book "Statistical Package for the
Social Sciences", second edition published by McGraw-Hill Book
Company.
As will be seen from the mean value of kappa numbers
measured in accordance with respective methods, a somewhat lower
numerical value was also obtained in these tests when carrying
out the method according to the invention. It will also be seen
that the dispersion in the measuring results obtained is
surprisingly small in both methods.
This shows-that when applying the method according to
the invention it is possible to obtain accurate information
concerning the lignin content of the pulp in a much shorter
time than was previously normal, calculated from the time at
which the pulp sample was extracted to the time at which the
kappa number is calculated, which greatly facilitates the
control of ~he different pulp-manufacturing stages.
