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Applied Real-Time Acoustic Chemometrics for Measurements of Canadian Standard Freeness
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
SCA Graphic Sundsvall AB.
2005 (English)In: Paperi ja puu, ISSN 0031-1243, Vol. 87, no 7, 452-457 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we present a method for measuring Canadian Standard Freeness (CSF) on-line in real-time using acoustic measurements. The method can be used to present a new CSF value every second. The higher measurement rate and the reduced time-delay compared to conventional pulp sensors make it a suitable tool for improved refiner control.

The method was developed during full-scale trials on two separate Sunds Defibrator double disc refiners at SCA Ortviken, Sweden. Acoustic measurements were performed using an accelerometer affixed to the refiner blow line. Trial conditions have been varied over a wide range of pulp quality and disturbances in the vibration signal. CSF was for example varied in the range 62-453 ml and refiner-housing pressure was varied from 0,35 to 0,39 MPa.

The vibration signals collected during I second were treated to yield power spectra that were used for all further work. A median spectrum was calculated for each experimental point and these spectra were combined with reference values for freeness to make up the calibration matrices. The spectra were pre-treated using Orthogonal Signal Correction (OSC) and Subsequently Partial Least Squares Regression (PLSR) was used to build models between spectra and freeness. For model validation leave-one-out cross validation has been used.

Over the range 90-250 ml we can predict CSF from median power spectra with a Root Mean Square Error of Prediction (RMSEP) of 23 ml. Over the larger CSF range of 62-453 mt the RMSEP deteriorates to 39 mt. Data from two separate trials on different refiners and from different seasons were included in these models.

Place, publisher, year, edition, pages
2005. Vol. 87, no 7, 452-457 p.
Keyword [en]
pulp quality control; CSF; TMP; process sensor; sound; acoustics; chemometrics; digital signal processing
National Category
Analytical Chemistry
URN: urn:nbn:se:kth:diva-7140ISI: 000233046600010ScopusID: 2-s2.0-27744580387OAI: diva2:12060
QC 20100629Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-12-03Bibliographically approved
In thesis
1. Chemometric and signal processing methods for real time monitoring and modeling: applications in the pulp and paper industry
Open this publication in new window or tab >>Chemometric and signal processing methods for real time monitoring and modeling: applications in the pulp and paper industry
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In the production of paper, the quality of the pulp is an important factor both for the productivity and for the final quality. Reliable real-time measurements of pulp quality are therefore needed. One way is to use acoustic or vibration sensors that give information-rich signals and place the sensors at suitable locations in a pulp production line. However, these sensors are not selective for the pulp properties of interest. Therefore, advanced signal processing and multivariate calibration are essential tools. The current work has been focused on the development of calibration routes for extraction of information from acoustic sensors and on signal processing algorithms for enhancing the information-selectivity for a specific pulp property or class of properties. Multivariate analysis methods like Principal Components Analysis (PCA), Partial Least Squares (PLS) and Orthogonal Signal Correction (OSC) have been used for visualization and calibration. Signal processing methods like Fast Fourier Transform (FFT), Fast Wavelet Transform (FWT) and Continuous Wavelet Transform (CWT) have been used in the development of novel signal processing algorithms for extraction of information from vibrationacoustic sensors.

It is shown that use of OSC combined with PLS for prediction of Canadian Standard Freeness (CSF) using FFT-spectra produced from vibration data on a Thermo Mechanical Pulping (TMP) process gives lower prediction errors and a more parsimonious model than PLS alone. The combination of FFT and PLS was also used for monitoring of beating of kraft pulp and for screen monitoring. When using regular FFT-spectra on process acoustic data the obtained information tend to overlap. To circumvent this two new signal processing methods were developed: Wavelet Transform Multi Resolution Spectra (WT-MRS) and Continuous Wavelet Transform Fibre Length Extraction (CWT-FLE). Applying WT-MRS gave PLS-models that were more parsimonious with lower prediction error for CSF than using regular FFT-Spectra. For a Medium Consistency (MC) pulp stream WT-MRS gave predictions errors comparable to the reference methods for CSF and Brightness. The CWT-FLE method was validated against a commercial fibre length analyzer and good agreement was obtained. The CWT-FLE-curves could therefore be used instead of other fibre distribution curves for process control. Further, the CWT-FLE curves were used for PLS modelling of tensile strength and optical parameters with good results.

In addition to the mentioned results a comprehensive overview of technologies used with acoustic sensors and related applications has been performed.

Abstract [sv]

Vid framställning av pappersprodukter är kvaliteten på massan en viktig faktor för produktiviteten och kvalitén på slutresultatet. Det är därför viktigt att ha tillgång till tillförlitliga mätningar av massakvalitet i realtid. En möjlighet är att använda akustik- eller vibrationssensorer i lämpliga positioner vid enhetsoperationer i massaprocessen. Selektiviteten hos dessa mätningar är emellertid relativt låg i synnerhet om mätningarna är passiva. Därför krävs avancerad signalbehandling och multivariat kalibrering. Det nu presenterade arbetet har varit fokuserat på kalibreringsmetoder för extraktion av information ur akustiska mätningar samt på algoritmer för signalbehandling som kan ge förbättrad informationsselektivitet. Multivariata metoder som Principal Component Analysis (PCA), Partial Least Squares (PLS) and Orthogonal Signal Correction (OSC) har använts för visualisering och kalibrering. Signalbehandlingsmetoderna Fast Fourier Transform (FFT), Fast Wavelet Transform (FWT) och Continuous Wavelet Transform (CWT) har använts i utvecklingen av nydanande metoder för signalbehandling anpassade till att extrahera information ur signaler från vibrations/akustiska sensorer.

En kombination av OSC och PLS applicerade på FFT-spektra från raffineringen i en Termo Mechnaical Pulping (TMP) process ger lägre prediktionsfel för Canadian Standard Freeness (CSF) än enbart PLS. Kombinationen av FFT och PLS har vidare använts för monitorering av malning av sulfatmassa och monitorering av silning. Ordinära FFT-spektra av t.ex. vibrationssignaler är delvis överlappande. För att komma runt detta har två signalbehandlingsmetoder utvecklats, Wavelet Transform Multi Resolution Spectra (WT-MRS) baserat på kombinationen av FWT och FFT samt Continuous Wavelet Transform Fibre Length Extraction (CWT-FLE) baserat på CWT. Tillämpning av WT-MRS gav enklare PLS-modeller med lägre prediktionsfel för CSF jämfört med att använda normala FFT-spektra. I en annan tillämpning på en massaström med relativt hög koncentration (Medium Consistency, MC) kunde prediktioner för CSF samt ljushet erhållas med prediktionsfel jämförbart med referensmetodernas fel. Metoden CWT-FLE validerades mot en kommersiell fiberlängdsmätare med god överensstämmelse. CWT-FLE-kurvorna skulle därför kunna användas i stället för andra fiberdistributionskurvor för processtyrning. Vidare användes CWT-FLE kurvor för PLS modellering av dragstyrka samt optiska egenskaper med goda resultat.

Utöver de nämnda resultaten har en omfattande litteratursammanställning gjorts över området och relaterade applikationer.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. xv, 113 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2007:33
Acoustic, Vibration, Multivariate, Chemometrics, PLS, OSC, PCA, FFT, Wavelets, WT-MRS, CWT-FLE, Pulp Quality, CSF, Brightness, Tensile Strength properties, Optical Properties, Measurement Technology, On-line, Non-invasive, Process Control, Process Analysis, Process Analytical Technology, PAT., Akustik, Vibrationer, Multivariat, Kemometri, PLS, OSC, PCA, FFT, Wavelets, WT-MRS, CWT-FLE, Massakvalitet, CSF, Ljushet, Dragstyrkeegenskaper, Optiska egenskaper, Mätteknik, On-line, Icke berörande mätning, Processtyrning, Processanalys, Processanalytisk Teknologi, PAT.
National Category
Analytical Chemistry
urn:nbn:se:kth:diva-4383 (URN)978-91-7178-679-1 (ISBN)
Public defence
2007-06-01, Sal K1, Teknikringen 56, Stockholm, 13:00
QC 20100629Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-06-29Bibliographically approved

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