Note: Descriptions are shown in the official language in which they were submitted.
1
METHOD AND MEASUREMENT APPARATUS FOR MEASURING SUSPENSION
Technical Field
The exemplary and non-limiting embodiments of the invention relate
generally to measurement of a wood fibre suspension.
Background
The following description of background art may include insights,
discoveries, understandings or disclosures, or associations together with
disclosures not known to the relevant art prior to the present invention but
provided by the invention. Some of such contributions of the invention may be
specifically pointed out below, whereas other such contributions of the
invention
will be apparent from their context.
In paper and pulp manufacturing the purpose is to obtain end product
having a good and uniform quality. To ensure the quality measurements are
performed during the manufacturing process. For example, lignin content of the
pulp is measured. The lignin content of a suspension such as pulp is usually
denoted with a kappa number_ in standard SCAN-C 1:77, which is known in the
field of pulp manufacturing, the kappa number is defined as the amount of
potassium permanganate solution with a concentration of 20 mmo1/1 in
millilitres
which one gram of dry pulp consumes in the conditions defined in the standard.
Another substance, which content in the pulp is has an effect on the
process and end product, is hexenuronie acid, often denoted as HexA.
The content of HexA from the pulp can be measured in laboratory
environment with known methods. However, laboratory measurements are
problematic as they typically take time from 30 minutes to hours) as in
manufacturing environments results should be obtained quickly in the different
process stages to enable control of the manufacturing process based on the
measurements. Thus there is a need for a solution which enables monitoring
HexA content during manufacturing phase.
Brief description
An object of the invention is to provide an improved method and an
apparatus implementing the method to reduce or avoid the above-mentioned
problems_
The objects of the invention are achieved by a method of measuring a
suspension which contains wood fibres, the method comprising: changing
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consistency of the suspension in a consistency range; directing optical
radiation
using a first optical wavelength and a second optical wavelength at the
suspension; measuring and determining a first intensity value of the optical
radiation within the consistency range related to the first optical wavelength
and
a second intensity value related to the second optical wavelength on at least
one
given consistency value; and determining the ratio of the first and second
intensity values; determining kappa number of the suspension; obtaining raw
value hexenuronic acid, HexA, by applying predetermined factors to the ratio
of
the first and second intensity values; and determining the content of
hexenuronic
acid, HexA, in the suspension by multiplying the raw value with the kappa
number.
The objects of the invention are achieved by a measurement apparatus
for measuring a suspension which contains wood fibres, the measurement
apparatus comprising one or more optical power sources for directing optical
is radiation
at the suspension and at least one optical measurement sensor for
measuring optical radiation interacted with the suspension, the measurement
apparatus being arranged to change consistency of the suspension in a
consistency range; direct optical radiation using a first optical wavelength
and a
second optical wavelength at the suspension; measure and determine a first
intensity value of the optical radiation within the consistency range related
to the
first optical wavelength and a second intensity value related to the second
optical
wavelength on at least one given consistency value; determine the ratio of the
first and second intensity values; determine kappa number of the suspension;
obtain a raw value hexenuronic acid, HexA, by applying predetermined factors
to
the ratio of the first and second intensity values; and determine the content
of
hexenuronic acid, HexA, in the suspension by multiplying the determined ratio
with the kappa number.
Brief description of the drawings
In the following the invention will be described in greater detail by
means of preferred embodiments with reference to the accompanying drawings,
in which
Figure 1 is a flowchart illustrating an example of an embodiment of the
invention;
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Figure 2 illustrates an example of a measurement arrangement
according to an embodiment;
Figure 3 illustrate an example of measurement arrangement;
Figures 4A, 413 and 4C illustrate examples of measurement
arrangement;
Figures 5A and 5B illustrate examples of measurement results;
Figure 6 illustrates the calibration of measurement apparatus;
Figure 7 illustrates an example of an apparatus configured to act as a
measurement controller and
Figure 8 illustrates an example of a measurement arrangement
according to an embodiment.
Detailed description of some embodiments
The solution according to the invention is particularly suitable for
measuring suspension which contains wood fibres, but it is by no means limited
to this.
In this application 'optical radiation' means electromagnetic radiation
with a wavelength of approximately 40 nm to 1 mm, and 'ultraviolet radiation'
means electromagnetic radiation with a wavelength of approximately 40 nm to
400 nm.
In the proposed solution, a suspension which contains wood fibres, is
exposed to optical radiation and interaction of the radiation with the
suspension
is measured while the consistency of the suspension is changed during the
measurement process.
Figure 1 is a flowchart illustrating an example of an embodiment of the
invention, where suspension which contains wood fibres is measured.
In step 100, consistency of the suspension is changed in a consistency
range. In an embodiment, the consistency range extends from an initial
consistency to a final consistency.
In step 102, optical radiation using a first optical wavelength 21 and a
second optical wavelength A.2 is directed at the suspension. In an embodiment,
the first optical wavelength is 23S nm SO urn and the second optical
wavelength
is 280 nm SO nm.
In step 104, a first intensity value of the optical radiation within the
consistency range related to the first optical wavelength and a second
intensity
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value related to the second optical wavelength is measured on at least one
given
consistency value.
In step 106, the ratio of the first and second intensity values is
determined. Thus, values IA1 and IA2 are obtained
Thus in an embodiment, intensity values are measured using two
different wavelengths on a given consistency value. A ratio of these
intensities is
determined.
In another embodiment, consistency of the suspension is changed so
that the consistency continuously goes through all consistencies in the
consistency range.
The intensity of optical radiation interacted with the suspension is
measured at different consistencies in the consistency range. The maximum
intensity of the optical radiation related to the first optical wavelength and
the
second optical wavelength is determined and the ratio of the maximum intensity
is of the
optical radiation related to the first optical wavelength to the maximum
intensity of the optical radiation related to the second optical wavelength is
determined. Thus, values lAlmax and IX2max are obtained.
Thus as the consistency of the suspension is changed from the initial
consistency to the final consistency the measurement is repeated at given
intervals using both first and second wavelength. The interval may be a
measurement parameter. As a result a value for intensity IA1 for the first
optical
wavelength Al and IA2 for the second optical wavelength IA2 are obtained.
In an embodiment, the optical radiation is directed to the suspension
using one or more optical power sources. There may be a power source for each
wavelength, or the wavelength of the radiation outputted by the source may be
changed or the wavelength if the radiation is selected using filters, for
example.
The intensity of optical radiation interacted with the suspension is
measured with one or more optical measurement sensors having a given surface
area and distance from the one or more optical power sources.
In an embodiment, the given surface area and distance are selected on
the basis of the consistency range and desired amount of intensity.
in an embodiment, the first optical wavelength and the second optical
wavelength arc within the ultraviolet radiation wavelength range.
in step 108, kappa number of the suspension is determined.
3S There are
various ways of determining the kappa number K. In an
embodiment, the kappa number of the suspension is determined based on one or
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both of the determined maximum intensity values IA.1max, IA2max. However, any
prior art method for determining the kappa number of the suspension may be
utilised here as well.
In step 110, a raw value for hexenuronic acid, HexARaw, is obtained by
applying predetermined factors to the determined ratio IA1/IA2 or
lAlmax/IA2max. The predetermined values calibrate the measurement results. An
example of obtaining the predetermined values is explained below in connection
with Figure 6.
In step 112, the content of hexenuronic acid, HexA, in the suspension is
determined by multiplying the raw value with the kappa number. Thus,
HexA = K * HexARaw or HexA = K * HexARaw.
HexA content in pulp may have an effect in kappa measurements.
HexA and lignin have different properties and cause different effects in
bleaching
of the manufacturing process. Thus knowledge of the HexA content is important.
is The oxidation phase of the manufacturing process HexA content is not
reduced as
the lignin content. Using C102 in the manufacturing process reduces both HexA
and lignin, but due to the high cost of C102 it is not a good choice for HexA
removal
as there are cheaper substances for removing HexA.
Next, an example of a measurement arrangement of an embodiment
will be described with reference to Figure 2, which shows application of the
invention in the pulp and paper industry.
Figure 2 shows a pipe 200 where a suspension 202 containing wood
fibres, i.e. wood fibre pulp, is flowing. A sample of the suspension is taken
with a
sampler 204 from the pipe 200. The sampler 202 may be a solution known per se,
e.g. based on a piston and a cylinder. The sample is conveyed using a pipe 206
to
a measurement chamber 208, valve 210 being closed.
The suspension in the measurement chamber may be processed prior
measurement. For example, liquid may be filtered by using pressured air. Valve
212 may be opened and the air coming through the valve presses the sample
against the wire 214 and liquid flows through valve 216.
The sample may be washed using water and air by opening valves 212
and 218, the waste water flows through the valve 216.
When the sample has been washed measurement process may start by
mixing the sample using pressured air through valve 220 and by adding water
through valve 222. When sample has been mixed air valve 220 is closed. Water
valve 222 is left open. Water comping through the valve changes the
consistency
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of the sample and at the same time mixes the sample. The consistency of the
suspension is changed in a consistency range. In an embodiment, the
consistency
range extends from an initial consistency to a final consistency.
Measuring may be performed during the chancing of the consistency of
the sample using measurement arrangement 224, 226 which may be controlled
by a measurement controller 228. In an embodiment, the measurement
arrangement comprises a source and detector part 226 and optical fibre and
measurement head part 226.
Figures 3 and 4A to 4C illustrate examples of measurement
arrangement 224, 226. In an embodiment, the arrangement comprises one or
more optical power sources 300. For simplicity, only one source is shown in
Figure 3. Measurements are usually made in the ultraviolet light, for which
reason
the optical power source may typically emit at least ultraviolet light. The
source
300 may be a Xenon lamp or a LED (light emitting diode), for example. The
optical
is power source direct may be configured to direct optical radiation at the
suspension. In an embodiment, the radiation is directed to the suspension
using
first optical fibre 306. The first optical fibre 306 may be configured to
direct the
optical radiation at the suspension, the first end of the fibre being
connected to
the optical light source 300 and the second end of the fibre, located at a
measurement head and being inserted in the measurement chamber 208.
In an embodiment, the arrangement further comprises one or more
detectors 302, 304 arranged to measure the intensity of optical radiation
interacted with the suspension. In an embodiment, each detector is connected
to
a set of optical fibres 308, 310, the ends of the optical fibres being
positioned next
to the second end of the first optical fibre 302.
Figure 4A to 4C illustrate examples of the fibre arrangement in the
measurement head 312 which may be inserted into the measurement chamber
208.
Figure 4A illustrates an embodiment, where the measurement
arrangement comprises the optical power source 300 connected to first optical
fibre 308 and detector 302 connected to optical fibre 308. At the measurement
head the first optical fibre 306 and the optical fibre 308 are located side by
side
with a given distance 400 from each other.
Figure 48 illustrates another embodiment, where the measurement
arrangement comprises the optical power source 300 connected to first optical
fibre 308 and detector 302 connected to a set of optical fibres 308. At the
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measurement head the ends of the optical fibres 308 are positioned next to the
end of the first optical fibre 306 at a same given distance 402 from the first
optical
fibre.
Figure 4C illustrates another embodiment, where the measurement
arrangement comprises the optical power source 300 connected to first optical
fibre 308 and detectors 302, 304 connected to a set of optical fibres 308,
310, At
the measurement head the ends of the optical fibres 308 are positioned next to
the end of the first optical fibre 306 at a same given distance 404 from the
first
optical fibre and the ends of the optical fibres 310 are positioned next to
the end
of the first optical fibre 306 at a same given distance 406 from the first
optical
fibre.
In an embodiment, the measurement chamber 208 comprises a
window 230 in the wall of the measurement chamber. The optical power source
300 or the first optical fibre 306 connected to the source may be placed
outside
the measurement chamber behind the window for directing optical radiation at
the suspension.
Likewise one or more detectors 302, 304 or optical fibres 308, 310
connected to the detectors may be placed outside the measurement chamber
behind the window 230 in the measurement chamber wall.
The use of optical fibres described above is merely an example. The
measurement may be realised also without optical fibres. In an embodiment, the
optical radiation is led to the measurement chamber using a radiation
conductor
such as a lens, a wave guide or any suitable medium. For example, the optical
source and detectors may be placed behind the window 230 without the use of
any optical fibres.
Figures 5A and 5B illustrate examples of measurement results when
the intensity of optical radiation interacted with suspension at different
consistencies is measured using above described measurement arrangement
using first optical wavelength and second optical wavelength. In the
nonlimiting
examples of Figure 5A and 5B the first optical wavelength is 235 nm and the
second optical wavelength is 280 nm. Depending on the embodiment the
wavelength may vary, for example by 50 nm.
Figure SA illustrates measurements made using the first optical
wavelength 235 nm. In the graph consistency is on the x-axis 500 and measured
intensity is on the y-axis 502. Figure 5B illustrates measurements made using
the
second optical wavelength 280 nm. In the graph consistency is on the x-axis
504
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and measured intensity is on the y-axis 506. The consistency of the suspension
sample is changed as a function of consistency. Typically, in the beginning
the
suspension is large and as more water is mixed with the sample the suspension
gets lower.
The consistency of the sample of the suspension is changed during
measurement process. Figures 5A and 5B show consistency on x-axis, where the
small consistency value is on the left and higher consistency value on the
right. In
the actual measurements process the consistency is large in the beginning and
as
water is added the consistency diminishes.
As optical radiation from the optical power source is directed to the
sample of the suspension, part of the radiation scatters from the wood fibres
to
the detector, part scatters elsewhere and part absorbs in lignin. At some
point, as
the consistency changes, there is a maximum value 508, 510, for the measured
intensity. The measurement arrangement may be configured to detect the
is maximum value 508, 510 of the intensity detected by the detector.
The consistency with which the maximum intensity is reached
depends on absorption. The greater the absorption the smaller the consistency
with which the maximum intensity occurs.
In an embodiment, the initial consistency of the consistency range
measurement depends on the properties of the suspension. The measurement
continues until the maximum intensity has been detected and is terminated when
the measured intensity is getting smaller after the maximum value.
In an embodiment, the measurement arrangement is calibrated to
function correctly by performing calibration measurements. These measurements
may be performed using a normalizing reference plate placed in front of the
measurement arrangement. In an embodiment, the calibration is performed using
reference pulp. Calibration is necessary before the measurement apparatus is
actually used and needs to be performed from time to time because the route of
optical radiation, for example, may change or the detector responses may
change
in the course of time. The reference pulp is wood fibre pulp whose properties
have been measured in the laboratory and stabilized with respect to time.
There
is reference pulp commercially available for calibration of the measurement
apparatus, e.g. Paprican standard reference pulp 5-96 from a Canadian
manufacturer.
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In an embodiment, the surface areas and numerical apertures of the
optical source and the detectors are selected on the basis of the consistency
range
of the suspension and desired amount of intensity.
In an embodiment, the distances 400, 402, 404, 406 and the surface
area of the cross sections and numerical apertures of optical for fibres or
sets of
optical fibres 306, 308 and 310 are selected on the basis of the consistency
range
of the suspension and desired amount of intensity.
The distances 400, 402, 404, 406 and the surface area of the cross
sections of optical for fibres or sets of optical fibres 306, 308 are denoted
in
following as measurement geometry. Measurement geometry relates to the
consistency range. When measurements are made, the consistency of the
suspension must be such that sample processing (washing of sample and
changing the consistency) are possible. If the consistency of the suspension
is too
large the sample processing may not succeed. On the other hand, if the
consistency is too low dynamics of the measurement suffers. Also available
intensity of light from the optical light source has an effect on the
measurements.
When kappa number is measured, the large the kappa is the more the lignin in
the
sample absorbs light.
In an embodiment, the purpose is to detect the maximum intensity of
the optical radiation interacted with the suspension within the consistency
range.
The consistency at which the maximum intensity is reached may depend on
following issues:
The distance 400, 402, 404, 406 between the optical power source and
the measurement point, i.e the distance between the end of the first
optical Ore 306 and the ends of other optical fibres 306, 308. The
larger the distance the smaller is the consistency when maximum
intensity occurs.
The surface areas of the optical power source and measurement
points. The larger the surface areas the smaller is the consistency
when maximum intensity occurs.
The kappa number of the sample. The larger the kappa number the
smaller is the consistency when maximum intensity occurs.
Wavelength of the radiation outputted by the optical power source.
Absorption of the radiation in the suspension depends on the
3S
wavelength. The larger the absorption the smaller is the consistency
when maximum intensity occurs.
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Particle size of the sample of the suspension. The smaller the particles,
the smaller is the consistency when maximum intensity occurs.
Thus in an embodiment, measurement parameters may comprise the
measurement geometry, the wavelength of the optical radiation and the
consistency range used in the measurements.
Further, the consistency range may depend on the properties of the
suspension. For example, when measuring pine suspension consistency range
may be 0.3-0.1% and when measuring birch suspension consistency range may
be 0.4-0.2%. These numerical values are only non-limiting examples.
Typical values for optical fibre diameters are around few hundred urn,
but also other values may be used depending on the property to be measured.
In general, the above discussion applies also when optical fibres are
not used but the optical source and detectors are connected to the measurement
chamber using some other suitable medium.
is In an
embodiment, as mentioned above in connection with Figure 1,
the ratio of the maximum intensity of the optical radiation related to the
first
optical wavelength to the maximum intensity of the optical radiation related
to
the second optical wavelength IXlmax/IA2max is determined.
Figure 8 illustrates an embodiment of a measurement arrangement. In
this example intensity values are measured in a measurement chamber. The
measurement arrangement comprises a measurement chamber 800 having
suspension with a given consistency. The arrangement comprises one or more
light sources 802, 804. In an embodiment, a light source may transmit light
with
multiple wavelengths, such a Xenon light source, for example. In an
embodiment,
there may be a light source for each wavelength. An example of a single
wavelength light source is a led. The arrangement further comprises one or
more
detectors 806, 808. In an embodiment, a detector may comprise a filter passing
through only a given wavelength. The filter may be changeable. This is
suitable
especially when the light source transmit multiple wavelengths. In an
embodiment, where the light source transmits only one wavelength a filter is
not
required.
Further, kappa number of the suspension is determined. In an
embodiment, the kappa number of the suspension is determined based on one or
both of the determined maximum intensity values IA.1max, IX2max. However, any
3S prior art
method for determining the kappa number of the suspension may be
utilised here as well.
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When the ratio of the first and second intensity values and kappa
number has been determined, a value for HexA may be determined. To calibrate
the measurement results predetermined factors are applied to the ratio and a
so
called raw HexA value is obtained. The HexA value in umol/g units is obtained
by
multiplying the raw HexA value with the kappa number.
Figure 6 illustrates an example of determining the predetermined
factors. In determining the factors, the consistency of the suspension is
changed
and the intensity is measured at two wavelengths, in this example 235 and 280
nm. The samples from which the intensity values are measured are taken also to
laboratory premises where kappa number and HexA value is determined using
laboratory procedures. Thus, for each intensity value ratio there exists a
Laboratory HexA and kappa values, which may be denoted as HexALAB and
KappaLAB. Figure 6 illustrates the relationship of ratio HexALAB/KappaLAB as a
function of ratio of intensity values. As can be seen, in this example, the
relationship follows a power function.
In a general form, the power function may denoted as y axb where y
equals HexALAB/KappaLAB and x equals IX1/IA.2 and where variables a and b are
the predetermined factors.
In the specific example of Figure 6, the power function is y =0.6561 x-
1.402.
Thus, when the relationship follows the above power function, the
RawHexA value may be obtained from the measured ratio of intensity values as
RawHexA = a * (1A1/IA2)b or RawHexA = a * (IA1max/I2max)b.
The power function is here used as an example only. Depending on the
situation, the relationship may also be a linear function, or a polynomial
function
or some other function which maps the ratio of intensity values to the ratio
HexALAB/KappaLAB.
In general, for each measurement apparatus, the determination of the
predetermined factors needs to be done only once if the configuration of the
apparatus or the suspension type (from one tree type to another, for example)
does not change. In an embodiment, the correctness of the factors may be
checked
from time to time using measurements.
Figure 7 illustrates an embodiment. The figure illustrates a simplified
example of an apparatus configured to act as a measurement controller 228.
It should be understood that the apparatus is depicted herein as an
example illustrating some embodiments. It is apparent to a person skilled in
the
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art that the apparatus may also comprise other functions and/or structures and
not all described functions and structures are required. Although the
apparatus
has been depicted as one entity, different modules and memory may be
implemented in one or more physical or logical entities.
The apparatus 228 of the example includes a control circuitry 700
configured to control at least part of the operation of the apparatus.
The apparatus may comprise a memory 702 for storing data.
Furthermore the memory may store software 704 executable by the control
circuitry 700. The memory may be integrated in the control circuitry.
The apparatus may further comprise an interface circuitry 706
configured to connect the apparatus to other devices. The interface may
provide a
wired or wireless connection. The interface may connect the apparatus to the
measurement arrangement 224, 226. In an embodiment, the apparatus may be
connected to an automatic process control computer used in the manufacture of
is pulp.
The apparatus may further comprise user interface 708 such as a dis-
play, a keyboard and a mouse, for example. In an embodiment, the apparatus
does
not comprise user interface but is connected to other devices providing access
to
the apparatus.
In some embodiments, the apparatus may be realised with a mini- or
microcomputer, a personal computer or a laptop or any suitable computing
device.
In an embodiment, intensity measurements and kappa measurements
may be performed in the same measurement chamber using different measuring
geometry. For example, in the solution of Figure 4C one detector may measure
kappa number and other intensity.
It will be obvious to a person skilled in the art that, as the technology
advances, the inventive concept can be implemented in various ways. The
invention and its embodiments are not limited to the examples described above
but may vary within the scope of the claims.
Date Recue/Date Received 2020-08-06
