| 1. |
- Forsström, Stefan, 1984-, et al.
(författare)
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Specialanpassade kurser för yrkesverksamma ingenjörer : Erfarenheter och upplevelser
- 2023
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Ingår i: Bidrag från den 9:e utvecklingskonferensen för Sveriges ingenjörsutbildningar. - : Mälardalens universitet. - 9789174856200 ; , s. 348-353
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- I dagens samhälle blir det allt viktigare att fortbilda sig under hela sitt yrkesverksamma liv. För att möta efterfrågan på det livslånga lärandet har Mittuniversitetet utvecklat och genomfört ett antal kurser som riktar sig mot yrkesverksamma ingenjörer. Detta arbete presenterar våra erfarenheter av att ge dessa kurser, med en tyngdpunkt på studenternas upplevelser. Syftet med detta är att bygga upp en vetenskaplig bas för vad vi gör som är bra, men även vad som kan förbättras och förändras. Målsättningen är att göra dessa specialanpassade kurser riktade mot yrkesverksamma ingenjörer så givande och flexibla som möjligt. Våra initiala resultat visar bland annat att studenternas negativa upplevelser ofta var kopplade till antagningsförfarandet och det praktiska genomförandet av kurserna. Man hade svårigheter med att hitta hur man skulle registrera sig på kursen och att tidsramen för registrering kunde vara ett problem. Läroplattformen uppfattades som svår att överblicka och det förekom även viss otydlighet gällande var undervisningen skulle äga rum. Den positiva responsen i utvärderingarna gällde främst det faktiska kursinnehållet, då man ansåg att uppgifter och kursmaterial var givande. Vidare uppskattades kursupplägget, att man kunde kombinera studierna med arbete. Framledes kommer vi att fortsätta med dessa utvärderingar i takt med att kurserna ges, och därefter anpassa vårt mottagande och kommunikationen med studenterna. Även kursupplägget ses över kontinuerligt via den återkoppling vi mottar.
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| 2. |
- Lindström, Stefan B, Professor, 1974-, et al.
(författare)
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Pulp Particle Classification Based on Optical Fiber Analysis and Machine Learning Techniques
- 2024
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Ingår i: Fibers. - : MDPI AG. - 2079-6439. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- In the pulp and paper industry, pulp testing is typically a labor-intensive process performed on hand-made laboratory sheets. Online quality control by automated image analysis and machine learning (ML) could provide a consistent, fast and cost-efficient alternative. In this study, four different supervised ML techniques—Lasso regression, support vector machine (SVM), feed-forward neural networks (FFNN), and recurrent neural networks (RNN)—were applied to fiber data obtained from fiber suspension micrographs analyzed by two separate image analysis software. With the built-in software of a commercial fiber analyzer optimized for speed, the maximum accuracy of 81% was achieved using the FFNN algorithm with Yeo–Johnson preprocessing. With an in-house algorithm adapted for ML by an extended set of particle attributes, a maximum accuracy of 96% was achieved with Lasso regression. A parameter capturing the average intensity of the particle in the micrograph, only available from the latter software, has a particularly strong predictive capability. The high accuracy and sensitivity of the ML results indicate that such a strategy could be very useful for quality control of fiber dispersions.
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| 3. |
- Engberg, Birgitta A., Docent, 1975-, et al.
(författare)
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Abrasive refining of spruce TMP and CTMP fibers
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 57-62
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Most of the earlier proposed ways to reduce energy con-sumption in high consistency refining requires operating at a small disc gap. However, a small gap is often associated with a severe fiber length reduction and often lead to unsta-ble refining and a small operational window. To address these issues, the idea of utilizing abrasive segments surfaces is here revisited. Abrasive refiner segments, consisting of abrasive surfaces in combinations with traditional bars and grooves or flat abrasive surfaces without any bars or grooves, were evaluated in both pilot and mill scale. From the trials it could be concluded, that particularly stable refin-ing was achieved with less power variations compared to when using standard segments, even when refining at very small disc gaps. The lw-mean fiber length of the pulps was not reduced or only slightly reduced, even when refining at very small disc gaps. Tensile index could be increased more efficiently or equally efficient as when using standard seg-ments. Improved energy efficiency could be achieved when combining the abrasive surface with high intensity treat-ment.
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| 4. |
- Engberg, Birgitta A., Docent, 1975-, et al.
(författare)
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New Sustainable Method to Produce Pulp Fibres ‐ Deep Eutectic Solvent‐Assisted Mechanical Pulping
- 2021
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Ingår i: Accelerating the progress towards the 2030 SDGs in times of crisis. - Östersund : Mittuniversitetet. - 9789189341173 ; , s. 2131-
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Konferensbidrag (refereegranskat)abstract
- Mechanical pulps are widely used in the manufacture of printing paper grades and also to a lesser extent in packaging materials and hygiene products. An advantage of mechanical pulps in general is the high yield (95‐97%) of the production processes, which implies a resource efficient way of producing fibre‐based products. A major drawback when producing mechanical pulps for printing qualities is the high electric energy consumption needed. However, the mechanical action associated with the liberation of fibres from the wood matrix can be facilitated if the middle lamella lignin is softened, leading to lower energy input and less fibre damages. The lignin can be softened by chemicals and high process temperatures, like in the chemi‐thermomechanical process (CTMP) and the high‐temperature‐chemi‐thermomechanical process (HT‐CTMP), where sodium sulphite is utilized. The pulps from these processes are best suited for packaging materials and tissue products. In this study, an alternate chemical treatment using deep eutectic solvents (DES) was explored. The DES used was bio‐based, non‐toxic, non‐corrosive, and could be recycled. The main goal was to facilitate the refining process and possibly create a new quality of mechanical pulp, not to remove lignin or hemicellulose. Wood chips were pre‐steamed and then soaked in DES, to ensure a sufficient impregnation. The conditions of the DES treatment were much less severe than those of a chemical pulping process, i.e. low temperature, neutral or nearly‐neutral pH, and a short residence time. The excess DES was removed by washing the chips with water before the chips where fed into a refiner. According to fibre quality analyses, the DES‐treated fibres were longer and less damaged than the control. The DES‐treated fibres also demonstrated significantly higher dewatering capacity than fibres without DES‐treatment produced at the same specific energy input in the refiner. These facts indicate that the fractures during fibre liberation to a higher extent occurred in the middle lamella, similar to when producing CTMP. A maintained high yield of the DES‐treated pulp was confirmed by chemical analysis. In conclusion, this initial study show that DES‐assisted mechanical pulping appears to be an interesting alternative for producing a mechanical pulp with different fibre properties. An aim for future work would be to tailor the DES‐treatment to alter fibre properties in a more controlled manner preferably so that market shares could be taken from the today dominating low‐yield (<50%) processes.
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| 5. |
- Fallahjoybari, Nima, et al.
(författare)
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CFD Simulation Of Pulp Flow In Rotating And Non-Rotating Grooves
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 24-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present study deals with the numerical simulation of softwood pulp flow in the rotating and non-rotating grooves in an aim to investigate the fluid flow and forces acting on a representative surface mounted in the groove. The viscosity of softwood pulp in different consistencies is available from the experimental measurements reported in the literature providing the opportunity to examine the effects of fiber consistency on the velocity and pressure distribution within the groove. The simulations are carried out in OpenFOAM for different values of gap thickness and angular velocity from which the pressure coefficient and shear forces values are obtained. It is found that the pressure increases at the stagnation point located at the gap entrance in the non-rotating groove due to tangential motion of the upper wall which induces the helical motion of the pulp flow in the groove’s cavity. However, such an effect is not observed in the rotating cavity close to the groove inlet. Meanwhile, by moving further along the channel length toward the outlet the helical motion is enhanced and an increase in the pressure is observed at the stagnation point. The shear forces over the representative surface are found to be independent of representative surface’s location and it is in the same level in the rotating and non-rotating grooves. In addition to the numerical simulations, an analytical discussion is also presented to provide a deeper understanding of pressure coefficient and shear forces variations with different parameters in the rotating and non-rotating grooves.
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| 6. |
- Ferritsius, Olof
(författare)
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Beyond averages – some aspects of how to describe a heterogeneous material, mechanical pulp, on particle level
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For a more profound understanding of how a process works, it is essential to have a relevant description of the material being processed. With this description, it will be easier to evaluate and control processes to produce more uniform products with the right properties. The focus of this thesis is on how to describe mechanical pulps in ways that reflect its character.Mechanical pulps are made from wood, a highly heterogeneous material. Common practice within the pulping industry and academy is to describe mechanical pulps and its wide variety of particles in terms of averages. The energy efficiency of the mechanical pulping process is usually calculated without taking into account the characteristics of the wood fed to the process. The main objective of the thesis is to explore ways to make more detailed descriptions of mechanical pulps. A second objective is to propose useful ways to visualise these descriptions.The studies were carried out in full-scale mill operations for TMP of publication grades and CTMP for board grades with Norwegian spruce as raw material. The particles in the pulps were analysed in an optical particle analyser for several properties such as length, curl, wall thickness, diameter,and external fibrillation for 10,000 to 60,000 particles per sample to cover their wide property variation. The data was analysed by factor analysis, a method to reduce the multidimensional data space, and also compared with data simulations.Several examples were identified where averages based on wide and skewed distributions may hide useful information and therefore result in misleading conclusions regarding the fibrous material and process performance. A method was developed to calculate the distribution of a common bonding factor, BIND (bonding indicator) for individual particles. This factor is calculated from external fibrillation, wall thickness and diameter measured in an optical particle analyser. Distributions of BIND is one way to characterize and visualise the heterogeneity of mechanical pulp. A characteristic BIND-distribution is set in the primary refiner stage, depending on both wood and process conditions and remains mostly intact through the process.It was demonstrated that both BIND-distributions and 4D maps of the measured property distributions could be used to assess the tails of the distributions (extreme values), energy efficiency, and fractionation efficiency in a new way. It was even possible to get a measure for energy efficiency for a primary stage refiner, since a method was developed where the wood raw material was evaluated in the same way as the pulp discharged from the refiner.It was demonstrated that the average length-length-weighted fibre length, commonly referred to as the average weight-weighted fibre length, is a relevant way to express the amount of long fibres, i.e. “length factor”. The commonly used average length-weighted fibre length may lead to erroneous conclusions. Through data simulations of curl and fibre length on particle level it was found that today’s analysers may underestimate the true length of the particles, especially if they are prone to be curled. As a result, theranking of pulps may be altered.It was concluded that although there is an ISO standard, or long-time used property, it does not necessarily imply that it is a relevant method. Misleading conclusions may be drawn based on current methods; here, modifications of these methods are suggested.The main contribution of this study is the finding that that a highly heterogeneous material such as mechanical pulps could be described in new ways through visualisation of data in 4D maps. These maps reveal casualconnections and more pertinent questions may be raised in thecommunication along the chain product-pulp-wood.Going beyond averages may reveal discrepancies in the process and material that were previously unknown, and lead to a more profound understanding. It seems that the mechanical pulping process can be even further simplified than previously expected. It has been concluded that to operate the process more efficiently, and for make products with just the right quality, the main focus should be on the raw material and the primary refiner stage from a heterogeneity point of view.
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| 7. |
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| 8. |
- Ferritsius, Olof, et al.
(författare)
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Heterogeneity of Thermomechanical and Chemi-thermomechanical Pulps described with distributions of an independent common bonding factor on particle level
- 2022
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 17:1, s. 763-784
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Tidskriftsartikel (refereegranskat)abstract
- Particles in mechanical pulp show a wide variety but are commonly described using averages and/or collective properties. The authors suggest using distributions of a common bonding factor, BIND (Bonding INDicator), for each particle. The BIND-distribution is based on factor analysis of particle diameter, wall thickness, and external fibrillation of several mechanical pulps measured in an optical analyser. A characteristic BIND-distribution is set in the primary refiner, depending on both wood and process conditions, and remains almost intact along the process. Double-disc refiners gave flatter distributions and lower amounts of fibres with extreme values than single-disc refiners. More refining increased the differences between fibres with low and high BIND. Hence, it is more difficult to develop fibres with lower BIND. Examples are given of how BIND-distributions may be used to assess energy efficiency, fractionation efficiency, and influence of raw material. Mill scale operations were studied for printing-grade thermomechanical pulp (TMP), and board-grade chemi-thermomechanical pulp (CTMP), both from spruce.
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| 9. |
- Ferritsius, Olof, et al.
(författare)
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Opportunities and challenges in describing the heterogeneity of fibres
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 28-33
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Particles in mechanical pulp are a heterogeneous popu-lation, but commonly described using averages based on wide and skewed distributions. It was found that these aver-ages may lead to erroneous conclusions regarding the char-acter of the material and also how the material has been de-veloped along the process. This study is based on measure-ments of individual particle dimensions (length, curl, and ex-ternal fibrillation) in mill operation of CTMP and TMP as detected in an optical analyser.
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| 10. |
- Lindström, Stefan B, Professor, 1974-, et al.
(författare)
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Multivariate lognormal mixture for pulp particle characterization
- 2024
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Ingår i: Cellulose. - : Springer Nature. - 0969-0239 .- 1572-882X. ; 31:3, s. 1843-1854
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for pulp particle characterization based on a truncated lognormal mixture (TLM) model, as motivated by size statistics of organisms. We use an optical fiber analyzer to measure the length–width distribution of kraft-cooked roundwood or sawmill sources, of chemi-thermomechanical pulp (CTMP) samples from roundwood or sawmill sources, and the same CTMP samples after kraft post-processing. Our results show that bimodal TLMs capture salient features of the investigated pulp particle distributions, by decomposition into a large-particle and a small-particle fraction. However, we find that fibers from sawmill sources, which have not undergone mechanical treatment, cannot be described by TLM, likely due to non-random sampling. Within the confines of our dataset, the TLM characterization predicts laboratory sheet properties more effectively than conventional averaging methods for pulp particle size distributions. The TLM characterization is intended as a tool for controlling the pulp production process towards higher product quality, uniformity, and energy efficiency, pending further mill trials for validation.
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| 11. |
- Liubytska, K, et al.
(författare)
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Elastic wave’s tail reconstruction in a split-Hopkinson bar
- 2023
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Ingår i: Book of Abstracts Euromech Colloquium 634.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The split Hopkinson pressure bar (SHPB) is a widely used method for analyzing the strength-strain characteristics of wood materials [1]. Experiments show that, as wood is a relatively soft material and the experimental setup is limited in size, the entire wave is not fully recorded before it is mixed with waves reflected from the ends. To be able to analyze how much energy is dissipated in a deformation process, it is required that the whole wave be recorded. In the present investigation, the pressure tail was reconstructed theoretically in the incident bar using the data from the transmission bar, which should allow for a reduction in the error in the energy of the waves.When a deformation wave propagates along bars, part of its energy dissipates into the environment. In this study, a modification of the SHPB was proposed to calculate and analyze the amount of energy the system loses, not due to the sample. Formulas for energy and momentum equilibrium were used [2]. The influence of the length of the striker and the level of input energy were also analyzed.In the presented experiment, all energy tails were completely recorded. This allowed for the theoretical reconstruction of the tail and a comparison with the recorded one. The pressure tail in the transmitted wave was manually shortened and replaced with a theoretical tail. The theoretical tail was created by performing an exponential curve fit with points from the tail up to the point where it had been shortened. The results show that only about 10% of the tail needs to be registered to accurately reconstruct it. When a registered wave is replaced with a reconstructed one, the resulting error in the total wave's energy value is no greater than 0.3% for a 500mm striker and 1.5% for a 250mm striker.
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| 12. |
- Persson, Johan, et al.
(författare)
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Feeding of double disc refiners – rotor design evaluation
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 69-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work presents a hypothesis of how steam flow effect the chip flow in the Double disc (DD) refiner and test it with a numerical simulation. DD refiners are often considered one of the most energy efficient refiner models. However, feeding chips into these machines is not as easy as feeding single disc refiners due to the rotating geometries. It is our belief that to increase energy efficiency in refining we need to increase also the production rates. The authors have previously noticed that in a standard DD rotor, steam flowed both in the same direction as the flow of woodchips and in the opposite direction. It is our hypothesis that backwards flowing steam in and in close proximity to the critical transition from the non-rotating geometry to the rotating geometry is negative for the material flow. To evaluate the hypothesis a new rotor was designed to eliminate the backwards flow. The authors have previously presented a two way coupled multiphase model with steam flow modeled with Computational Fluid Dynamics and wood chips modeled as groups of connected spherical particles with Discrete Element Method with a momentum exchange model. This model was utilized to model the flow of steam and woodchips in a DD under normal operational parameters, with the conventional rotor and with the new rotor. The throughput of wood chips was evaluated and normalized with regards to the chip flow to the refiner. The flow was considerable more stable in the new rotor, the throughput was close to 100 % for the observed time window, and the steam flow was more uniform. The results of the simulation supports the hypothesis. The next step in the research would be to test the new rotor in full scale operation.
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| 13. |
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