SE1950243A1 - Method and measurement apparatus for measuring suspension - Google Patents

Method and measurement apparatus for measuring suspension

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Publication number
SE1950243A1
SE1950243A1 SE1950243A SE1950243A SE1950243A1 SE 1950243 A1 SE1950243 A1 SE 1950243A1 SE 1950243 A SE1950243 A SE 1950243A SE 1950243 A SE1950243 A SE 1950243A SE 1950243 A1 SE1950243 A1 SE 1950243A1
Authority
SE
Sweden
Prior art keywords
optical
suspension
intensity
consistency
wavelength
Prior art date
Application number
SE1950243A
Other languages
Swedish (sv)
Other versions
SE542895C2 (en
Inventor
Matti Törmänen
Mikko Haapalainen
Pasi Kärki
Original Assignee
Valmet Automation Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Automation Oy filed Critical Valmet Automation Oy
Publication of SE1950243A1 publication Critical patent/SE1950243A1/en
Publication of SE542895C2 publication Critical patent/SE542895C2/en

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
    • D21G9/00—Other accessories for paper-making machines
    • D21G9/0009—Paper-making control systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/34—Paper
    • G01N33/343—Paper paper pulp
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C7/00—Digesters
    • D21C7/12—Devices for regulating or controlling
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
    • D21H23/78—Controlling or regulating not limited to any particular process or apparatus
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • G01N21/474—Details of optical heads therefor, e.g. using optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/51—Scattering, i.e. diffuse reflection within a body or fluid inside a container, e.g. in an ampoule
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0028—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at baseband stage
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N2021/3196—Correlating located peaks in spectrum with reference data, e.g. fingerprint data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • G01N21/474—Details of optical heads therefor, e.g. using optical fibres
    • G01N2021/4742—Details of optical heads therefor, e.g. using optical fibres comprising optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • G01N2021/4764—Special kinds of physical applications
    • G01N2021/4769—Fluid samples, e.g. slurries, granulates; Compressible powdery of fibrous samples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N2021/8405—Application to two-phase or mixed materials, e.g. gas dissolved in liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N2021/8411—Application to online plant, process monitoring
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N2021/8444—Fibrous material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/30—Circuits for homodyne or synchrodyne receivers
    • H04B2001/305—Circuits for homodyne or synchrodyne receivers using dc offset compensation techniques

Abstract

The invention relates to method of measuring a suspension which contains wood fibres. The consistency of the suspension is changed (100) in a consistency range. Optical radiation using a first optical wavelength and a second optical wavelength is directed (102) at the suspension. A first intensity value of the optical radiation related to the first optical wavelength and a second intensity value related to the second optical wavelength on at least one given consistency value is determined (104). The ratio of the first and second intensity values is determined (106). Kappa number of the suspension is determined (108). A raw value for hexenuronic acid, HexA is obtained (110) by applying predetermined factors to the ratio of the first and second intensity values. The content of HexA in the suspension is determined (112) by multiplying the determined ratio with the kappa number.

Description

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 withdisclosures not known to the relevant art prior to the present invention butprovided by the invention. Some of such contributions of the invention may bespecifically pointed out below, whereas other such contributions of the inventionwill be apparent from their context. ln paper and pulp manufacturing the purpose is to obtain end producthaving a good and uniform quality. To ensure the quality measurements areperformed during the manufacturing process. For example, lignin content of thepulp is measured. The lignin content of a suspension such as pulp is usuallydenoted with a kappa number. ln standard SCAN-C 1:77, which is known in thefield of pulp manufacturing, the kappa number is defined as the amount ofpotassium permanganate solution with a concentration of 20 mmol/l in millilitreswhich 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 theprocess and end product, is hexenuronic acid, often denoted as HexA.
The content of HexA from the pulp can be measured in laboratoryenvironment with known methods. However, laboratory measurements areproblematic as they typically take time (from 30 minutes to hours) as inmanufacturing environments results should be obtained quickly in the differentprocess stages to enable control of the manufacturing process based on themeasurements. Thus there is a need for a solution which enables monitoring HexA content during manufacturing phase.
Brief descriptionAn object of the invention is to provide an improved method and anapparatus implementing the method to reduce or avoid the above-mentioned problems.
The objects of the invention are achieved by method as claimed inclaim 1 and by apparatus as claimed in claim 10. Some embodiments of the invention are disclosed in the dependent claims.
Brief description of the drawings ln the following the invention will be described in greater detail bymeans of preferred embodiments with reference to the accompanying drawings,in which Figure 1 is a flowchart illustrating an example of an embodiment oftheinvention; Figure 2 illustrates an example of a measurement arrangementaccording to an embodiment; Figure 3 illustrate an example of measurement arrangement; Figures 4A, 4B and 4C arrangement] illustrate examples of measurement 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 ameasurement 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 formeasuring suspension which contains wood fibres, but it is by no means limitedto this. ln this application 'optical radiation' means electromagnetic radiationwith a wavelength of approximately 40 nm to 1 mm, and 'ultraviolet radiation'means electromagnetic radiation with a wavelength of approximately 40 nm to400 nm. ln the proposed solution, a suspension which contains wood fibres, isexposed to optical radiation and interaction of the radiation with the suspensionis measured while the consistency of the suspension is changed during themeasurement process.
Figure 1 is a flowchart illustrating an example of an embodiment ofthe invention, where suspension which contains wood fibres is measured. ln step 100, consistency of the suspension is changed in a consistencyrange. ln an embodiment, the consistency range extends from an initialconsistency to a final consistency. ln step 102, optical radiation using a first optical wavelength Ål and asecond optical wavelength ÄZ is directed at the suspension. ln an embodiment,the first optical wavelength is 235 nm i 50 nm and the second optical wavelengthis 280 nm i 50 nm. ln step 104, a first intensity value of the optical radiation within theconsistency range related to the first optical wavelength and a second intensityvalue related to the second optical wavelength is measured on at least one givenconsistency value. ln step 106, the ratio of the first and second intensity values isdetermined. Thus, values IÄ1 and IÄZ are obtained Thus in an embodiment, intensity values are measured using twodifferent wavelengths on a given consistency value. A ratio of these intensities isdetermined. ln another embodiment, consistency of the suspension is changed sothat the consistency continuously goes through all consistencies in theconsistency range.
The intensity of optical radiation interacted with the suspension ismeasured at different consistencies in the consistency range. The maximumintensity of the optical radiation related to the first optical wavelength and thesecond optical wavelength is determined and the ratio of the maximum intensityof the optical radiation related to the first optical wavelength to the maximumintensity of the optical radiation related to the second optical wavelength isdetermined. Thus, values lÄlmax and lÄ2max are obtained.
Thus as the consistency of the suspension is changed from the initialconsistency to the final consistency the measurement is repeated at givenintervals using both first and second wavelength. The interval may be ameasurement parameter. As a result a value for intensity IÄ1 for the first opticalwavelength Ål and IÄZ for the second optical wavelength IÄZ are obtained. ln an embodiment, the optical radiation is directed to the suspensionusing one or more optical power sources. There may be a power source for eachwavelength, 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 ismeasured with one or more optical measurement sensors having a given surfacearea and distance from the one or more optical power sources. ln an embodiment, the given surface area and distance are selected onthe basis of the consistency range and desired amount of intensity. ln an embodiment, the first optical wavelength and the second opticalwavelength are within the ultraviolet radiation wavelength range. ln step 108, kappa number ofthe suspension is determined.
There are various ways of determining the kappa number K. ln anembodiment, the kappa number of the suspension is determined based on one orboth of the determined maximum intensity values lÄ1max, lÄ2max. However, anyprior art method for determining the kappa number of the suspension may beutilised here as well. ln step 110, a raw value for hexenuronic acid, HexARaw, is obtained byDtl/IÄZ or lÄ1max/lÄ2max. The predetermined values calibrate the measurement results. An applying predetermined factors to the determined ratioexample of obtaining the predetermined values is explained below in connectionwith Figure 6. ln step 112, the content of hexenuronic acid, HexA, in the suspension isdetermined 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 bleachingof the manufacturing process. Thus knowledge of the HexA content is important.The oxidation phase of the manufacturing process HexA content is not reduced asthe lignin content. Using C102 in the manufacturing process reduces both HexAand lignin, but due to the high cost of C102 it is not a good choice for HexA removalas there are cheaper substances for removing HexA.
Next, an example of a measurement arrangement of an embodimentwill be described with reference to Figure 2, which shows application of theinvention in the pulp and paper industry.
Figure 2 shows a pipe 200 where a suspension 202 containing woodfibres, i.e. wood fibre pulp, is flowing. A sample of the suspension is taken with asampler 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 priormeasurement. For example, liquid may be filtered by using pressured air. Valve212 may be opened and the air coming through the valve presses the sampleagainst the wire 214 and liquid flows through valve 216.
The sample may be washed using water and air by opening valves 212and 218, the waste water flows through the valve 216.
When the sample has been washed measurement process may start bymixing the sample using pressured air through valve 220 and by adding waterthrough valve 222. When sample has been mixed air valve 220 is closed. Watervalve 222 is left open. Water comping through the valve changes the consistencyof the sample and at the same time mixes the sample. The consistency of thesuspension is changed in a consistency range. ln an embodiment, the consistencyrange extends from an initial consistency to a final consistency.
Measuring may be performed during the chancing of the consistency ofthe sample using measurement arrangement 224, 226 which may be controlledby a measurement controller 228. ln an embodiment, the measurementarrangement comprises a source and detector part 226 and optical fibre andmeasurement head part 226.
Figures 3 and 4A to 4C illustrate examples of measurementarrangement 224, 226. ln an embodiment, the arrangement comprises one ormore optical power sources 300. For simplicity, only one source is shown inFigure 3. Measurements are usually made in the ultraviolet light, for which reasonthe optical power source may typically emit at least ultraviolet light. The source300 may be a Xenon lamp or a LED (light emitting diode), for example. The opticalpower source direct may be configured to direct optical radiation at thesuspension. ln an embodiment, the radiation is directed to the suspension usingfirst optical fibre 306. The first optical fibre 306 may be configured to direct theoptical radiation at the suspension, the first end of the fibre being connected tothe optical light source 300 and the second end of the fibre, located at ameasurement head and being inserted in the measurement chamber 208. ln an embodiment, the arrangement further comprises one or moredetectors 302, 304 arranged to measure the intensity of optical radiationinteracted with the suspension. ln an embodiment, each detector is connected toa set of optical fibres 308, 310, the ends ofthe optical fibres being positioned nextto the second end of the first optical fibre 302.
Figure 4A to 4C illustrate examples of the fibre arrangement in themeasurement head 312 which may be inserted into the measurement chamber208.
Figure 4A illustrates an embodiment, where the measurementarrangement comprises the optical power source 300 connected to first opticalfibre 308 and detector 302 connected to optical fibre 308. At the measurementhead the first optical fibre 306 and the optical fibre 308 are located side by sidewith a given distance 400 from each other.
Figure 4B illustrates another embodiment, where the measurementarrangement comprises the optical power source 300 connected to first opticalfibre 308 and detector 302 connected to a set of optical fibres 308. At themeasurement head the ends of the optical fibres 308 are positioned next to theend of the first optical fibre 306 at a same given distance 402 from the first opticalfibre.
Figure 4C illustrates another embodiment, where the measurementarrangement comprises the optical power source 300 connected to first opticalfibre 308 and detectors 302, 304 connected to a set of optical fibres 308, 310. Atthe measurement head the ends of the optical fibres 308 are positioned next tothe end of the first optical fibre 306 at a same given distance 404 from the firstoptical fibre and the ends of the optical fibres 310 are positioned next to the endof the first optical fibre 306 at a same given distance 406 from the first opticalfibre. ln an embodiment, the measurement chamber 208 comprises awindow 230 in the wall of the measurement chamber. The optical power source300 or the first optical fibre 306 connected to the source may be placed outsidethe measurement chamber behind the window for directing optical radiation atthe suspension.
Likewise one or more detectors 302, 304 or optical fibres 308, 310connected to the detectors may be placed outside the measurement chamberbehind the window 230 in the measurement chamber wall.
The use of optical fibres described above is merely an example. Themeasurement may be realised also without optical fibres. ln an embodiment, theoptical radiation is led to the measurement chamber using a radiation conductorsuch as a lens, a wave guide or any suitable medium. For example, the opticalsource 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 whenthe intensity of optical radiation interacted with suspension at differentconsistencies is measured using above described measurement arrangementusing first optical wavelength and second optical wavelength. ln the nonlimitingexamples of Figure 5A and 5B the first optical wavelength is 235 nm and thesecond optical wavelength is 280 nm. Depending on the embodiment thewavelength may vary, for example by i 50 nm.
Figure 5A illustrates measurements made using the first opticalwavelength 235 nm. ln the graph consistency is on the x-axis 500 and measuredintensity is on the y-axis 502. Figure 5B illustrates measurements made using thesecond optical wavelength 280 nm. ln the graph consistency is on the x-axis 504and measured intensity is on the y-axis 506. The consistency of the suspensionsample is changed as a function of consistency. Typically, in the beginning thesuspension is large and as more water is mixed with the sample the suspensiongets lower.
The consistency of the sample of the suspension is changed duringmeasurement process. Figures 5A and 5B show consistency on x-axis, where thesmall consistency value is on the left and higher consistency value on the right. lnthe actual measurements process the consistency is large in the beginning and aswater is added the consistency diminishes.
As optical radiation from the optical power source is directed to thesample of the suspension, part of the radiation scatters from the wood fibres tothe detector, part scatters elsewhere and part absorbs in lignin. At some point, asthe consistency changes, there is a maximum value 508, 510, for the measuredintensity. The measurement arrangement may be configured to detect themaximum value 508, 510 ofthe intensity detected by the detector.
The consistency with which the maximum intensity is reacheddepends on absorption. The greater the absorption the smaller the consistencywith which the maximum intensity occurs. ln an embodiment, the initial consistency of the consistency rangemeasurement depends on the properties of the suspension. The measurementcontinues until the maximum intensity has been detected and is terminated whenthe measured intensity is getting smaller after the maximum value. ln an embodiment, the measurement arrangement is calibrated tofunction correctly by performing calibration measurements. These measurements may be performed using a normalizing reference plate placed in front of the measurement arrangement. ln an embodiment, the calibration is performed usingreference pulp. Calibration is necessary before the measurement apparatus isactually used and needs to be performed from time to time because the route ofoptical radiation, for example, may change or the detector responses may changein the course of time. The reference pulp is wood fibre pulp whose propertieshave been measured in the laboratory and stabilized with respect to time. Thereis reference pulp commercially available for calibration of the measurementapparatus, e.g. Paprican standard reference pulp 5-96 from a Canadianmanufacturer. ln an embodiment, the surface areas and numerical apertures of theoptical source and the detectors are selected on the basis ofthe consistency rangeofthe suspension and desired amount ofintensity. ln an embodiment, the distances 400, 402, 404, 406 and the surfacearea of the cross sections and numerical apertures of optical for fibres or sets ofoptical fibres 306, 308 and 310 are selected on the basis of the consistency rangeofthe suspension and desired amount of intensity.
The distances 400, 402, 404, 406 and the surface area of the crosssections of optical for fibres or sets of optical fibres 306, 308 are denoted infollowing as measurement geometry. Measurement geometry relates to theconsistency range. When measurements are made, the consistency of thesuspension must be such that sample processing (washing of sample andchanging the consistency) are possible. lf the consistency ofthe suspension is toolarge the sample processing may not succeed. On the other hand, if theconsistency is too low dynamics of the measurement suffers. Also availableintensity 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 thesample absorbs light. ln an embodiment, the purpose is to detect the maximum intensity ofthe optical radiation interacted with the suspension within the consistency range.The consistency at which the maximum intensity is reached may depend onfollowing issues: - The distance 400, 402, 404, 406 between the optical power source andthe measurement point, i.e the distance between the end of the firstoptical fibre 306 and the ends of other optical fibres 306, 308. Thelarger the distance the smaller is the consistency when maximum intensity occurs.
- The surface areas of the optical power source and measurementpoints. The larger the surface areas the smaller is the consistencywhen maximum intensity occurs.
- The kappa number of the sample. The larger the kappa number thesmaller 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 thewavelength. The larger the absorption the smaller is the consistencywhen maximum intensity occurs.
- Particle size ofthe sample ofthe suspension. The smaller the particles,the smaller is the consistency when maximum intensity occurs.
Thus in an embodiment, measurement parameters may comprise themeasurement geometry, the wavelength of the optical radiation and theconsistency range used in the measurements.
Further, the consistency range may depend on the properties of thesuspension. For example, when measuring pine suspension consistency rangemay be 0.3-0.1% and when measuring birch suspension consistency range maybe 0.4-0.2°/o. These numerical values are only non-limiting examples.
Typical values for optical fibre diameters are around few hundred um,but also other values may be used depending on the property to be measured. ln general, the above discussion applies also when optical fibres arenot used but the optical source and detectors are connected to the measurementchamber using some other suitable medium. ln an embodiment, as mentioned above in connection with Figure 1,the ratio of the maximum intensity of the optical radiation related to the firstoptical wavelength to the maximum intensity of the optical radiation related tothe second optical wavelength lÄ1max/lÄ2max is determined.
Figure 8 illustrates an embodiment of a measurement arrangement. lnthis example intensity values are measured in a measurement chamber. Themeasurement arrangement comprises a measurement chamber 800 havingsuspension with a given consistency. The arrangement comprises one or morelight sources 802, 804. ln an embodiment, a light source may transmit light withmultiple wavelengths, such a Xenon light source, for example. ln an embodiment,there may be a light source for each wavelength. An example of a singlewavelength light source is a led. The arrangement further comprises one or more detectors 806, 808. ln an embodiment, a detector may comprise a filter passing through only a given wavelength. The filter may be changeable. This is suitableespecially when the light source transmit multiple wavelengths. ln anembodiment, where the light source transmits only one wavelength a filter is notrequired.
Further, kappa number of the suspension is determined. ln anembodiment, the kappa number of the suspension is determined based on one orboth of the determined maximum intensity values Dtlmax, lÄ2max. However, anyprior art method for determining the kappa number of the suspension may beutilised here as well.
When the ratio of the first and second intensity values and kappanumber has been determined, a value for HexA may be determined. To calibratethe measurement results predetermined factors are applied to the ratio and a socalled raw HexA value is obtained. The HexA value in umol/g units is obtained bymultiplying the raw HexA value with the kappa number.
Figure 6 illustrates an example of determining the predeterminedfactors. ln determining the factors, the consistency of the suspension is changedand the intensity is measured at two wavelengths, in this example 235 and 280nm. The samples from which the intensity values are measured are taken also tolaboratory premises where kappa number and HexA value is determined usinglaboratory procedures. Thus, for each intensity value ratio there exists aLaboratory HexA and kappa values, which may be denoted as HexALAB andKappaLAB. Figure 6 illustrates the relationship of ratio HexALAB/KappaLAB as afunction of ratio of intensity values. As can be seen, in this example, therelationship follows a power function. ln a general form, the power function may denoted as y = axb where yequals HexALAB/KappaLAB and x equals lÄl/IÄZ and where variables a and b arethe predetermined factors. ln 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, theRawHexA value may be obtained from the measured ratio of intensity values as RawHexA = a * (lÄl/IÄZP or RawHexA = a * (l7t1max/lÄ2max)b.
The power function is here used as an example only. Depending on thesituation, the relationship may also be a linear function, or a polynomial functionor some other function which maps the ratio of intensity values to the ratioHexALAB/KappaLAB. 11 ln general, for each measurement apparatus, the determination of thepredetermined factors needs to be done only once if the configuration of theapparatus or the suspension type (from one tree type to another, for example)does not change. ln an embodiment, the correctness of the factors may be checkedfrom time to time using measurements.
Figure 7 illustrates an embodiment. The figure illustrates a simplifiedexample of an apparatus configured to act as a measurement controller 228. lt should be understood that the apparatus is depicted herein as anexample illustrating some embodiments. lt is apparent to a person skilled in theart that the apparatus may also comprise other functions and/or structures andnot all described functions and structures are required. Although the apparatushas been depicted as one entity, different modules and memory may beimplemented in one or more physical or logical entities.
The apparatus 228 of the example includes a control circuitry 700configured 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 controlcircuitry 700. The memory may be integrated in the control circuitry.
The apparatus may further comprise an interface circuitry 706configured to connect the apparatus to other devices. The interface may provide aWired or wireless connection. The interface may connect the apparatus to themeasurement arrangement 224, 226. ln an embodiment, the apparatus may beconnected to an automatic process control computer used in the manufacture ofpulp.
The apparatus may further comprise user interface 708 such as a dis-play, a keyboard and a mouse, for example. ln an embodiment, the apparatus doesnot comprise user interface but is connected to other devices providing access tothe apparatus. ln some embodiments, the apparatus may be realised with a mini- ormicrocomputer, a personal computer or a laptop or any suitable computingdevice. ln an embodiment, intensity measurements and kappa measurementsmay be performed in the same measurement chamber using different measuringgeometry. For example, in the solution of Figure 4C one detector may measure kappa number and other intensity. 12 lt will be obvious to a person skilled in the art that, as the technologyadvances, the inventive concept can be implemented in various ways. Theinvention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims (17)

13 Claims
1. A method of measuring a suspension which contains wood fibres,the method comprising: changing (100) consistency ofthe suspension in a consistency range; directing (102) optical radiation using a first optical wavelength and asecond optical wavelength at the suspension; measuring and determining (104) a first intensity value of the opticalradiation within the consistency range related to the first optical wavelength anda second intensity value related to the second optical wavelength on at least onegiven consistency value; and determining (106) the ratio ofthe first and second intensity values; determining (108) kappa number of the suspension; characterisedby obtaining (110) a raw value hexenuronic acid, HexA, by applyingpredetermined factors to the ratio of the first and second intensity values; and determining (112) the content of hexenuronic acid, HexA, in the suspension by multiplying the raw value with the kappa number.
2. The method as claimed in claim 1, further comprising: directing the optical radiation to the suspension using an opticalpower source; and measuring the intensity of optical radiation interacted with thesuspension with one or more optical measurement sensors having a given surface area, numerical aperture and distance from the optical power source.
3. The method as claimed in claim 1 or 2, wherein the first opticalwavelength and the second optical wavelength are within the ultraviolet radiation wavelength range.
4. The method as claimed in any previous claim 1 to 3, wherein thefirst optical wavelength is 235 nm i 50 nm and the second optical wavelength is280 nm i 50 nm. 14
5. The method as claimed in any preceding claim 1 to 4, furthercomprising: changing the consistency of the suspension so that the consistencycontinuously goes through all consistencies in the consistency range, measuring the intensity of optical radiation interacted with thesuspension at different consistencies in the consistency range; determining the maximum intensity of the optical radiation related tothe first optical wavelength and the second optical wavelength; and determining the ratio of the maximum intensity of the optical radiationrelated to the first optical wavelength to the maximum intensity of the optical radiation related to the second optical wavelength.
6. The method as claimed in any preceding claim 1 to 5, furthercomprising:taking a sample of suspension to be measured to an unpressurised measurement chamber.
7. The method as claimed in any previous claim 1 to 6, furthercomprising: directing the optical radiation at the suspension using a first opticalfibre having a given diameter and numerical aperture and measuring the intensity of optical radiation interacted with thesuspension with a detector connected to a set of optical fibres, each optical fibrehaving a given diameter, and the ends of the optical fibres being positioned nextto the end of the first optical fibre at a same given distance from the first opticalfibre.
8. The method as claimed in any previous claim 1 to 7, furthercomprising: directing the optical radiation at the suspension using one or morelight sources placed outside the measurement chamber behind a window in ameasurement chamber wall; and measuring the intensity of optical radiation interacted with thesuspension with a detector placed outside the measurement chamber behind awindow in a measurement chamber, the detector having a given diameter, and located a given distance from the one or more light sources.
9. The method as claimed in any previous claim 1 to 8, furthercomprising: measuring the intensity of optical radiation interacted with thesuspension at different consistencies in the consistency range using the firstoptical wavelength and the second optical wavelength; obtaining HexALab and KappaLab which denote the HexA value andkappa number of the suspension at the same consistencies determined atlaboratory; determining a function which maps the ratio of the measured first andsecond intensity values to the relation of HexALab and KappaLab; determining the predetermined factors on the basis of the function.
10. A measurement apparatus for measuring a suspension whichcontains wood fibres, the measurement apparatus comprising one or moreoptical power sources (300) for directing optical radiation at the suspension andat least one optical measurement sensor (302) for measuring optical radiationinteracted with the suspension, the measurement apparatus being arranged to change (100) consistency ofthe suspension in a consistency range; direct (102) optical radiation using a first optical wavelength and asecond optical wavelength at the suspension ; measure and determine (104) a first intensity value of the opticalradiation within the consistency range related to the first optical wavelength anda second intensity value related to the second optical wavelength on at least onegiven consistency value; determine (106) the ratio ofthe first and second intensity values; determine (108) kappa number ofthe suspension; characterised bythe measurement apparatus being further arranged to obtain (110) a raw value hexenuronic acid, HexA, by applyingpredetermined factors to the ratio of the first and second intensity values; and determine (112) the content of hexenuronic acid, HexA, in the suspension by multiplying the determined ratio with the kappa number.
11. The apparatus as claimed in claim 10, wherein:at least one measurement sensor has a given surface area, numerical aperture and distance from the one or more optical power sources, the given 16 surface area and distance being selected on the basis ofthe consistency range and desired amount of intensity.
12. The apparatus as claimed in any previous claim 10 to 11, whereinthe one or more optical power sources are configured to output the first opticalwavelength and the second optical wavelength which are within the ultraviolet radiation wavelength range.
13. The apparatus as claimed in any previous claim 10 to 12, whereinthe one or more optical power sources are configured to output first opticalwavelength having the value of 235 nm i 20 nm and the second optical wavelength having the value of 280 nm i 20 nm.
14. The apparatus as claimed in any previous claim 10 to 13, furtherconfigured to change the consistency of the suspension so that the consistencycontinuously goes through all consistencies in the consistency range measure the intensity of optical radiation interacted with thesuspension at different consistencies in the consistency range; determine the maximum intensity of the optical radiation related tothe first optical wavelength and the second optical wavelength; and determine the ratio of the maximum intensity of the optical radiationrelated to the first optical wavelength to the maximum intensity of the optical radiation related to the second optical wavelength.
15. The apparatus as claimed in any previous claim 10to 14, furthercomprising: a first optical fibre (306) configured to direct the optical radiation atthe suspension, the first end of the fibre being connected to the optical lightsource (300) and the second end of the fibre being in the measurement chamber;and one or more detectors (302) for measuring the intensity of opticalradiation interacted with the suspension, each detector being connected to a setof optical fibres (308), each optical fibre having a given diameter, and the ends ofthe optical fibres being positioned next to the second end of the first optical fibre at a same given distance from the first optical fibre (306), the given diameter and 17 distance being selected on the basis of the consistency range and desired amount of intensity.
16. The apparatus as claimed in any previous claim 10 to 14, furthercomprising a window (230) in a measurement chamber wall, the optical powersource being placed outside the measurement chamber (208) behind the windowin wall for directing the optical radiation at the suspension; and one or more detectors (302) for measuring the intensity of opticalradiation interacted with the suspension, the detectors being placed outside themeasurement chamber behind the window (230) in the measurement chamberwall, each detector having a given diameter, and located a given distance from theoptical power source (300), the given diameter and distance being selected on the basis of the consistency range and desired amount of intensity.
17. The apparatus as claimed in any previous claim 10 to 16, furthercomprising measuring the intensity of optical radiation interacted with thesuspension at different consistencies in the consistency range using the firstoptical wavelength and the second optical wavelength; obtaining HexALab and KappaLab which denote the HexA value andkappa number of the suspension at the same consistencies determined atlaboratory; determining a function which maps the ratio of the measured first andsecond intensity values to the relation of HexALab and KappaLab; determining the predetermined factors on the basis of the function.
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