James Olson

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
On low consistency refining of mechanical pulps (2019)

The aim of this thesis is to develop comprehensive knowledge to fill the gaps in the understanding of three key aspects of low consistency refining of mechanical pulps.Firstly, the fibre shortening mechanisms are formally studied by using a comminution model. Fibre length distribution data from before and after refining with a variety of pulp types, net-powers, feed flow rates, angular velocities and plate geometries was analyzed. Fibres' cutting rate and cutting location were found to be highly correlated with refiner gap. Plate geometry was also demonstrated to have a role in the fibre cutting location. Secondly, the relationship between net-power and gap was described using a correlation built entirely from pilot-scale refining data. Results showed that a properly defined dimensionless net-power number is crucial to compare different refiner sizes under the same grounds. The developed correlation was compared to industrial-scale data showing that the correlation is well suited for predictions. Key assumptions of the correlation were validated using bar-force sensor measurements data. Finally, the framework developed in the first two parts of this thesis were used together with pressure screening models available in literature to theoretically analyze refining systems typically found in TMP lines. Fibre length was used to assess each system performance in terms of refiner gap, reject ratio and refiner power. Moreover, the impact of some design aspects such as refiner size, recirculation and split-ratios was also described.

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Hydrodynamics of the hydrocyclone flow field : effects of turbulence modelling, geometrical and design parameters (2017)

This thesis describes a numerical study of the effect of swirl on the flow hydrodynamics in hydrocyclones and rotating pipes. Kinetic (force balance) and kinematic (velocity field) analysis were performed to identify the relative importance of turbulence, convective, and pressure forces in these flows. We showed that convective and pressure forces in hydrocyclones are three orders of magnitude larger than the size of turbulent forces, and seven orders of magnitude greater than the viscous forces. We derived a new dimensionless parameter based on a ratio of Euler numbers that gave a unique relationship for pressure along the axis of a hydrocyclone for all the cone angles tested. This finding enables rigorous scaling of hydrocyclones of differing cone angles.A complementary numerical study of flow in rotating pipes was carried out to elucidate the relative importance of convection and turbulence. We identified a dimensionless rotation parameter that delineates the condition at which decreasing turbulence force equals increasing convective force as rotational speed increases. This dimensionless number establishes a criterion for knowing which forces are dominant, and thereby a rational basis for choosing CFD (Computational Fluid Dynamics) models that are both cost-effective and accurate.Lastly, we conducted a sensitivity study to determine the effects of varying values of constants in the quadratic pressure-strain (QPS) Reynolds Stress turbulence model (RSM) for CFD modelling of swirl in hydrocyclones. The results identified the changes necessary to attain accurate predictions, such as overcoming the under-prediction problems of RSM. In addition, these findings laid the groundwork for a swirl-specific turbulence model for hydrocyclones.

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Energy and paper recycling : an investigation of repulping (2016)

Fibers from waste paper are recovered through repulping. Repulping is accomplished using machines called repulpers. Repulpers are large machines which use a high-speed rotor mounted in a vat to disintegrate waste paper for the recovery of fibers. Repulpers consume a significant amount of energy to recover fibers from waste paper. For the work in this thesis, a 0.25m³ laboratory repulper was built for the purpose of determining which variables affect the specific energy (energy/mass) required for repulping. Scale replicas of 3 commercial repulper rotors were constructed to test the effect of rotor geometry on repulping specific energy. It was found that the flake content as a function of specific energy follows the form dF⁄dE=-λF where F is flake content, E is specific energy, and λ is a rate constant. The rate constant λ varies with pulp type, temperature, consistency, repulper volume, and rotor design. It was found that a given material at a given temperature and consistency requires a unique quantity of energy to be repulped independent of the rate of energy addition. An analytical model for repulping linking pulp material properties, consistency, temperature, and rotor and vat geometry is provided which allows for the accurate prediction of the time and energy required for repulping in both the 0.25m³ laboratory scale repulper and a 15m³ industrial repulper. The model assumes that all work to deflake is done by the repulper rotor in the rotor swept volume by turbulence and that no deflaking occurs in the rest of the vat. CFD simulations of the flow field produced by each rotor and high-speed film of each rotor indicate that the rotors tested in this thesis all produce strong trailing vortices akin to those produced by common mixing impellers like the Rushton turbine. Uniform mixing is important for efficient repulping. Solid body motion of the suspension in the repulper makes for poor repulping energy efficiency. Repulping time and energy savings can be accomplished by increasing the suspension consistency and the rotor swept-volume/vat volume ratio by either increasing rotor size or reducing vat volume all while ensuring complete mixing and circulation in the vat.

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Observation of transition from laminar plug to well-mixed flow of fibre suspensions in Hagen-Poiseuille flow (2016)

The focus of the present work is an experimental study of the transition to turbulent flow of papermaking fibres in a cylindrical pipe. The suspensions used in this study possess a yield stress. With this class of fluid the radial profile in fully developed slow flow is characterized by an unyielded or plug zone. With increasing flow rates the size of the plug diminishes. One of the open remaining questions with these suspensions is the role of the plug during transition. In this work we characterize the size of the plug using ultrasound Doppler velocimetry as a function of flowrate for dilute, i.e. less than 2% consistency papermaking suspensions in a 50mm diameter pipe. The plug size was determined through analysis of local spatial and temporal variations in velocity, strain-rate, and the fluctuating component of velocity. With these we were able to estimate the yield stress of the suspension through knowledge of the applied pressure gradient and find the yield stress to be in the range of 2-60 Pa, depending upon consistency, fibre type and manufacturing methodology. The yield stress measurements were benchmarked against measurement methodologies reported in the literature. During flow, we observe complex behavior with the plug in which we found that with increasing velocity the plug diminishes through a densification mechanism in response to increasing frictional pressure drop. At higher Re, it diminishes through an erosion type mechanism. We estimate the critical Reynolds number for the disappearance of the plug to be Rec 10⁵. In perhaps the most unique measurements in this work we find that drag reduction begins when rp/R
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Low consistency refining of mechanical pulp : the relationship between plate pattern, operational variables and pulp properties (2014)

In this dissertation we propose a framework to predict pulp properties of mean fibre length and freeness from low consistency (LC) refiner operating conditions and present correlations between those properties of pulp and hand sheet paper properties of tear, tensile and bulk. This framework is not new and was proposed by Luukkonen [1] however, studying the effect of plate pattern in this work based on the methodology presented in this dissertation is a novel approach. We accomplish this objective through the introduction of two geometrical parameters: Bar InteractionLength, BIL, and Bar Interaction Area, BIA.To do so, a comprehensive modelling of the geometry of disc refiner plates used in LC refining of mechanical pulp is done. We develop analytical and numerical models to estimate important geometrical parameters such as bar crossing area, leading edges of bar crossings and number of crossing points in a disc refiner with parallel distribution of bars. We will then use these models to predict pulp properties of mean fibre length and freeness from refiner operating conditions by running pilotscalerefining trials of mechanical pulp over a wide range of plate pattern, rotational speed and gap size. From this stage, we present correlations between hand sheet paper properties of tear, tensile, bulk and pulp properties of freeness and fibre length.We also demonstrate a relationship between net power, plate pattern and refiner operating parameters such as plate gap and rotational speed based upon a classicaldimensional analysis in which a reduced parameter space is related to each other through the use of statistical modelling.

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Modelling Latency Removal of Mechanical Pulping Processes (2014)

No abstract available.

The effects of turbulent drag reducing additives on hydrocyclone operation : an evaluation of the flow behaviour and particle mechanics (2014)

The effects of adding drag reducing additives to a pulp processing hydrocyclone were experimentally investigated. This work was found to contribute towards improving particle separation efficiencies and reducing energy consumption. To effectively evaluate the performance improvements, the flow field was initially measured using laser Doppler velocimetry. In the presence of a particulate phase, the motions of variously sized particles were measured using a three dimensional, dual camera set-up. Quantification of the drag reducing potential of the various polymer solutions and fibre suspensions studied was experimentally determined using an integral analysis for a fixed control volume.The addition of drag reducing polymer additives was found to fundamentally change the hydrocyclone flow field from what is classically observed with water alone. For the conditions studied in this work, the effectiveness of a hydrocyclone towards removing contaminants would likely be reduced, as a particles separation zone was limited. The addition of polymer additives to a hydrocyclone was found to increase the size of particles susceptible to overflow removal. It was found that particles of density 1280 kg/m³ and diameter 500 - 600 microns displayed inwards motion in a 0.03% APAM solution, where purely outwards motion was measured for identically sized particles suspended in water. The flow field, however, indicated that overflow removal is limited to only a small region near the vortex finder.Polymer additives were found to be effective in reducing energy consumption in a hydrocyclone. Maximum drag reduction was found to occur at a reject ratio of 50% for polymer solutions, independent of inlet velocity. The energy savings potential for polymer additives in a pulp processing hydrocyclone, however, was found to be limited to the inlet velocity. Most in process hydrocyclones operate well above the minimum inlet velocities measured for rejects ratios of 25% and 50%, suggesting that additional energy savings would likely occur. The phenomenological degradation of the polymer agents investigated in this work suggests that the practical use of these additives would be difficult. This was found to be most significant with cellulose fibre suspensions containing cationic polyacrylamide (CPAM), as polymer adsorption resulted in rapid polymer degradation.

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Understanding of no-load power in low consistency refining (2014)

Low Consistency (LC) refining is the primary means of improving the strength and smoothness of paper by imparting energy to fibres through repeated fibre-bar interactions. The useful part of the energy modifies the morphology of the fibres and the remaining, no-load power, mainly overcomes the hydraulic, pumping and mechanical losses in the refiner. This thesis is aimed to explore the no-load power in LC refining both experimentally and computationally. The contribution of this thesis comes in three parts.Firstly, the effect of consistency, operational and plate design parameters on noload power was experimentally determined on two pilot scale LC refiners with different plate diameters. The obtained data were used to provide a statistical model for prediction of no-load power. To study the effect of diameter and groove depth, the no-load power consumption of some mills corresponding to their operating conditions, and the specifications of the relevant refiner discs were collected. Based on this model, no-load power is described in terms of two main components, hydraulic and pumpingpowers, and an empirical equation is proposed.Secondly, we numerically examined the two-dimensional flow of a Newtonian fluid in the gap formed between two opposing cavities which represent the cross-sectional flow in LC refiner. A large number of unsteady simulations were conducted to characterize the effect of gap size on the flow field over the range of velocities. Then, weexamined material transport between the cavities by introducing a passive scalar to represent the motion of tracer particles. Over the range of parameters studied, we identify two characteristic flow fields, defined as either steady or unsteady. We also find that particles are transported to the region near the leading edges of the bars only under the conditions of unsteady flow.Thirdly, we extended the numerical study by characterizing the effect of cavity depth on the flow field over the range of velocities. We find that the aspect ratio of the cavity dictates three characteristic flow fields based on the number of vortices formed within cavity and we propose criteria for cavity aspect ratio in terms of therefiner application.

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Modeling the maximum capacity of a pulp pressure screen (2013)

Pressure screens are used as a means of separating pulp fibres from contaminants. They are also used to improve pulp quality by fractionating fibres by length. Both functions are limited by the capacity of the device. Three studies were conducted in this thesis to understand the factors that affect maximum capacity.Capacity is determined by the complex hydrodynamics in the region between the screen rotor and the screen wall. To better understand this flow, the stream-wise velocity and aperture velocities were measured using particle image velocimetry. The vortex generated above the aperture and its size is shown to be strongly dependent on the aperture velocity, wall roughness and, to some extent, on the rotor speed. The vortex diminishes in size at higher aperture velocities that increase the exit layer height. The experiments also show that the reversal flow through the slot decreased with lower rotor speeds and increased slot velocities. This observation challenges the existing models of apertures being cleared simply by flow reversal driven by a suction pulse caused by flow acceleration between the foil and cylinder. In its place, this study identifies elements of a more sophisticated flow model that considers such factors as the depletion of the zone below the rotor and flow disturbances in the wake of the foil.The effects of screen cylinder geometry, pulp type, rotor and flow velocities on capacity were also investigated. Five types of screen cylinders were tested using different ratios of softwood/hardwood kraft pulp and different reject rates. It was found that the average fibre length has a significant impact on capacity. A comprehensive understanding of pulp screen capacity remains elusive. The present research has, however, provided insights which move away from the simplistic ''backflush'' models used in the past and supports a more sophisticated model that also considers: 1) the dynamics of fibre accumulation and removal rates of the slot entry, 2) the importance of a small-scale perturbations created by turbulent flow for fibre removal, and 3) the mechanics of fibre trapping on the downstream edge of the slot. These advancements also provide some direction for future equipment developments.

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Development of a methodology to optimize low consistency refining of mechanical pulp (2011)

In this dissertation we present a novel two-stage procedure to relate low consistency (LC) refiner operating conditions to changes in fibre morphology. To do so, a large database of operating conditions and resulting pulp properties were collected over a range of both pilot and industrial LC refiners operating with mechanical pulps. In total eight different Andritz TwinFlo™ were sampled over a three year period in both North America and Scandinavia. The two-stage methodology is based upon a classical dimensional analysis in which a reduced parameter space is related to each other through the use of statistical modelling. In the first stage we demonstrate a relationship between net power and operating parameters such as gap, rotational speed, diameter, plate pattern and consistency of the fibre suspension. For all refiners tested the model indicates that the net power increases nearly linearly with the inverse of gap size. In this portion of the analysis we found statistically significant relationships between operating conditions and suspension properties such as change in fibre length and Canadian Standard Freeness, an industrial standard related to pulp dewatering. In the second stage of this methodology, we build upon the work of Forgacs [1] and demonstrate that most paper properties, e.g. the mechanical strength, are related primarily to fibre length and freeness; over 80% of all variation in the data can be attributed to these two parameters. With this novel framework, in conjunction with the statistical models, we demonstrate that an optimum operating condition exist to maximize strength, and demonstrate the sensitivity of this relationship using a number of different type pulps. In the second portion of the thesis, we further develop a novel mechanical pulping process in which multiple stages of LC refining replace the second stage HC refining in a conventional TMP process. This work is motivated from the need to reduce electrical energy consumption to produce mechanical pulp. Using the two-stage methodology developed in the first portion of the thesis, we demonstrate under pilot plant conditions an energy savings of over 20% in comparison to a conventional TMP process to generate mechanical pulp of equal quality.

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Fractionation of particle suspensions in a viscoplastic fluid : towards a novel process (2011)

The focus of this thesis is the separation or sorting of particle suspensions in a yield stress or viscoplastic fluid. Although the process is applicable to most industrial suspensions, the motivation of the work stems from pulp and paper industry,i.e. papermaking and microfibrillated cellulose (MFC) suspensions. The work is presented in four different yet complementary studies.In the first study, the concept of particle fractionation in a viscoplastic fluid is introduced. Here this novel principle is demonstrated, batch wise, by measuringthe difference in centrifugal force required to initiate motion of an initially stable particle suspension in a gel. The criteria for motion is delineated as the ratio of the centrifugal force to yield stress as a function of particle size and orientation. Demonstration experiments are given to illustrate that the separation process is very efficient. In the second and third studies we demonstrate the principle on two industrial suspensions, i.e. a SBK (semi-bleached kraft) papermaking fibre and MFC. With papermaking fibres, it is shown that efficient separation, based upon cell wall thickness can be achieved. With MFC, it is shown that the process is more efficient than traditional separation techniques, i.e hydrocyclone and pressure screen. In the final study, we speculate regarding the conditions required to make a continuous process based upon the batch testings. Here, it is identified that a spiral Poiseuille flow would be sufficient to achieve separation. The questions addressed in this study are what is the size of the unyielded region for this flow field and what is the bound for transition to turbulent flow. It was found that the magnitude of the swirling flow does not affect the size of the plug and the axialvelocity is decoupled from the rotational rate. In addition, the yielded region is always formed in the middle of the annular gap. To address the flow state, a linear stability analysis was performed using the method of normal modes. The flow was found to be linearly stable for all conditions tested.

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A numerical and experimental investigation into pressure screen foil rotor hydrodynamics (2009)

Pressure screens are an effective way to remove contaminants from a pulp stream and to fractionate the pulp, or separate the fibres by length, both of which improve the quality of the end-product paper. In this thesis, seven experimental and numerical studies were conducted to investigate the hydrodynamics of pressure screen foil rotors and the effects of rotor design on the overall performance of a pressure screen. Additionally, this knowledge was applied to the development of a high performance foil rotor for both out-flow and in-flow screens.A multi-element foil rotor was developed using computational fluid dynamics (CFD), laboratory experiments, pilot plant trials, and a full scale mill trial. It was found that varying the shape and configuration of the foil affected both the pressure pulses generated by the rotor and the maximum capacity of the pressure screen. The multi-element foil (MEF) was found to be capable of generating a 126% higher magnitude negative pressure pulse, a 31% increase in screen capacity at a given rotor power consumption and a 43% reduction in power consumption without affecting capacity compared to state of the art single element rotors.The effect of varying the frequency of the pressure pulses, by changing the number of foils on the rotor, the diameter of the cylinder, and slot velocity on rotor performance was also studied. Adding foils to the rotor was found to reduce the velocity of the fluid relative to the foils and the magnitude of the pressure pulses generated by the rotors, leading to a reduction in overall screen performance. Increasing the diameter of the screen slightly reduces the performance of the foils. Increasing slot velocity did not affect the pressure pulses generated by the rotor for fully attached flows, but caused the foils to stall and a higher tip speed.Finally, factors affecting rotor power consumption other than rotor speed were investigated experimentally and analytically. The cylinder slot geometry, flow rates, and the design of the inlet to the screen were all found to have significant effects on rotor power consumption.

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Measurement of heterogeneity in low consistency pulp refining by comminution modeling (2009)

In pulp refiners, pulp in suspension flows through an annulus between a rotor and stator having surfaces with bars which impose cyclic loading on the pulp during bar crossings. This process has long been known to be heterogeneous in its treatment of pulp. However, there is no method available to measure heterogeneity of treatment in operating refiners. The objective of this thesis was to develop such a method.The approach was based on applying comminution theory and measurements of fibre length before and after refining. Specifically, measurements of fibre shortening were used to obtain two key parameters in the comminution differential equation: the selection function and the breakage function. A procedure was employed to account for breakage at any point along a fibre length instead of an arbitrary point as in previous studies. The selection function was expressed as the product of two factors: a probability of impact and a probability that intensity of an impacted fibre exceeded the rupture intensity. These probabilities were expressed in terms of refiner variables. Values for the selection and breakage functions were obtained by regression fitting to fibre length data. These length distribution data were obtained for a range of operating conditions in various refiner types. Findings for predicted numbers of impacts and intensities were consistent with the findings of previous studies.The probabilities derived from the selection and breakage functions gave distributions of numbers and intensities of impacts. The findings showed, for example, that homogeneity of treatment is more dependent on numbers of impacts than on uniformity of intensity during impacts. A single number “homogeneity index” was proposed and defined as the product of the number of impacts on fibres having length-weighted average and the probability of intensity being within +/- 2kJ/kg of the mean divided by the specific energy. Using this definition, it was shown that homogeneity of refining treatment increased with flow rate through the refiner and decreased with increasing groove depth and consistency. It also showed the degree to which increased residence time of fibres in a refiner could compensate for a coarse bar pattern in attaining homogeneity of treatment.

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The Orientation of Semi-Dilute Rigid Fibre Suspensions in a Linearly Contracting Channel (2008)

No abstract available.

Master's Student Supervision (2010 - 2018)
Artificial vegetation : a novel paper-based sound absorber (2018)

Demand for acoustic barriers in urban buildings grown in recent times fed by levels of increasing urban noise. Extraneous urban noise in buildings was commonly controlled using noise barriers like absorptive panels. The efficiency and sustainability of such noise absorbers is suspect. Our research in acoustics led to the development of a novel paper-based sound absorbers as a viable alternative for those currently available in the market. We named this product Artificial Vegetation (AV). We tested AV and found it an efficient and sustainable alternative that can be mass produced with relatively comparable low overheads. In this research paper we explored literature in acoustic barriers, both paper- and foam-based. We also identified gaps in the literature. The paper elaborates measurement of sound absorption coefficient using impedance-tube method, as a basic procedure for producing AV. We developed an analytical model that optimizes and improves sound absorptivity of AV. Data gathered from experiments were used to validate our model and test as a computational platform in more AV designs.

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Cellulose-Mycelia foam : novel bio-composite material (2017)

Demand for sustainable products is growing faster than ever before. Because of this, the development of novel sustainable materials is crucial to leverage our environmental resources and to ensure future growth of Canada's economy. In this study, we propose a technology to develop the use of fungal mycelium, the vegetative part of a fungus, through a porous scaffold of cellulose-based foam. A methodology for producing cellulose-mycelia foam (CMF) has been developed by mixing a surfactant with pulp suspension of 1% consistency and Pleurotus djamor spawn, mixing at high velocity to entrain air, filtering the suspension, and then holding at incubation conditions suitable for mycelium growth. During the incubation period, temperature (20-25 °C), pH (5-8), humidity (80-100%), ventilation and exposure to light were controlled. Simplicity of production, biodegradability, and 3-D porous structure of the product position this biocomposite as a green alternative to polymeric foams. The structure of the CMF was characterized through fluorescent microscopy during the incubation period. The effect of mycelial growth on the mechanical behavior of the CMF including compressibility, thermal decomposition, dry and wet strength was investigated during 25 days of mycelial growth. The results indicated that all tested mechanical properties improved after 25 days of mycelial growth. The second set of experiments was run to specify the application of the CMF in a hydraulic filtration system. The pressure drop, permeability, and filtration efficiency of the product were studied. The experimental results showed that the permeability of the CMF decreases by an increase in mycelial growth. The hydraulic filtration efficiency of the product improved from 74% for cellulosic foam to 99.9% for 25 days CMF for removing 20 µm and larger particles. Bioremediation tests also were performed to evaluate the detoxification capability of mycelia in the CMF. Detoxification tests demonstrated that the living mycelia are able to detoxify potassium hydroxide from waste alkaline batteries.

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The effects of anisotropic turbulence on fibre motion (2017)

No abstract available.

A novel algorithm for model plant mismatch detection for model predictive controllers (2016)

For Model Predictive Controlled (MPC) plants, the quality of the plant model determines the quality of performance of the controller. Model Plant Mismatch (MPM), the discrepancies between the plant model and actual plant transfer matrix, can both improve or degrade controller “performance”, depending on the context in which “performance” is defined. Instead of using simple, “yes-no” type of performance metrics to diagnose whether MPM is present, this thesis achieves the further goal of pinpointing the exact plant inputs causing MPM. The detection method consists of a two-step identification procedure. The first experiment identifies the MPM-affected rows in the plant matrix. The second experiment pinpoints the exact inputs causing said MPM, and these MPM-affected elements are further ascertained using a hypothesis test. Finally, using input design, an estimated optimal excitation sequence is generated based on the available closed-loop data, which helps the engineer determine whether the original excitation was sufficient for the aforementioned sys-ID experiments. The most important underlying assumptions are the linear time-invariance of the plant and noise dynamics. The proposed algorithm is exercised on artificial 3x3 and 5x5 plants, then on real data from an industrial lime slaker suffering from sparse MPM, to demonstrate its ability of accurately pinpointing MPM-affected elements.

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Origami engineering : advanced converting for novel paper products (2015)

The recent work has focused to develop a fully automated prototype in order to make products in large quantities. A unique and novel methodology has been developed to create self-folding paper products. This platform technology enables us to create sophisticated complex 3D paper structure from ordinary 2D paper sheet. The self-folding material is composed of pre-cut and creased paper and heat shrinking thermoplastic polymer. A computational drawing tool is first used to design folds for particular 3D shape then a computer numerical controller cutter with knife at variable pressure is employed to cut paper and the thermoplastic polymer. The cut paper and thermoplastic polymer can be attached together by a large number of polymeric materials and several means of attaching polymer-paper have been explored. The effect of various polymer-paper attachments including chemical adhesion, stitching and welding was studied. Heat welding procedure was quite successful and it showed to be promising technique to make a strong polymer-paper bond. An experimental device was made and a series of experiments were conducted to reveal the significant factors, their effective range, and their impact on the paper-polymer bond strength. The effect of pressure, temperature, welding attachment area and, thickness of paper on the paper-polymer bond strength were determined and a database of strength attachments with an effective factors variation was collected.First, our in-house developed servo-robot for cutting was assisted with automatic welding system and then a large flatbed cutter has been used and functionally changed to perform cutting, creasing and adhering paper and plastic in one step. The effect of significant factors such as attachment distance to fold line, heating temperature and paper thickness on the folding angle has been studied and discussed in chapter 4. Several examples of folded decorative and industrial products have been developed using this technique and introduced in chapter 5.

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An experimental study of fluid flow in a low consistency refiner (2014)

Transport phenomena inside a low consistency disc refiner were experimentally investigated. A transparent refiner door was designed and fabricated with four acrylic viewports enabling plate-scale and groove-scale visual observation. High speed video, ultra-violet fluorescent tracer particles and a MATLAB program were used to perform particle tracking velocimetry to gain further understanding of the flow field. The experimental working fluid under study was water. The effects of refiner operating parameters on the flow field were of particular interest. Refiner flow rates were varied from 300 to 700 litres per minute. Refiner rotational speeds were varied from 400 to 1200 RPM. Plate gap values under study included 7.5, 2.5, 1.5, and 0.75 mm. Two plate configurations were studied, including a smooth rotor and grooved rotor with a machined acrylic stator plate. The plate geometry under test was designed for softwood pulp having a bar edge length equal to 0.99 km/rev. A set of phenomenological characterizations of observed particle behaviour was identified. Qualitative results were provided for the effect of gap, refiner speed, and flow rate on the flow field. Lagrangian pathlines were shown to reveal tortuous flow for grooved rotor experiments. Quantitative results were presented for grooved rotor experiments for gaps of 0.75 mm. Eulerian measurements of groove axial velocity indicated fluid transport into and out of the stator grooves, while net transport occurred out of the grooves. The presence of backflow in the stator grooves was observed at all operating points for the grooved rotor under test. The relationship between stator backflow velocity and operating parameters was reported showing an increase with refiner speed and a minimal decrease with refiner flow rate. It has been shown that there is a linear relationship between stator backflow velocities and the pressure differential across the refiner. Rotational motion in the stator grooves was quantified by angular velocity and turnover rate of the fluid. Turnover rate was defined as the number of rotations of the fluid as it travels the length of the groove. Angular velocity increased proportionally with refiner speed and turnover rate did not vary significantly with refiner operating parameters.

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A study on the structure of paper : the links between paper and fibre properties (2013)

The work shown in this thesis, focuses on the effects of fibre geometry (fibre length, width and coarseness) to the paper strength and bulk. It is believed that fibre networks, for a given furnish, can be optimized through fractionation to create a stronger and bulkier paper. A first set of experiments was performed to determine the correlations among fibre properties of a softwood kraft pulp furnish. The fibre properties were measured using a Fibre Quality Analyzer (FQA). Coarseness (ω) and width (D) were found to increase linearly with length (Lf ). These correlations are thought to be influenced by the tree species and the pulping process. A second set of experiments was aimed to determine empirical expressions of bulk and tensile index (TI) in terms of the fibre geometry distribution (ω, Lf and D) and the press-drying pressure (P). Bulk and TI was measured for handsheets made at different pressures from different size distributions. These distributions were created by a combination of fractionation on a Bauer McNett Classifier (BMC) and fibre cutting. The determined relations show agreement with experimental work from other researchers. In order to provide insight into the causes of such behavior, simulations of two-dimensional (2D) and three-dimensional (3D) random networks were performed. Matlab was used to write the simulation codes. Mechanical response of fibres (affected by the fibre geometry) to the forces induced by drying or pressure is not considered directly in the simulations. However, 2D simulation models are a good representation of high press-drying conditions and high fibre flexibility, whereas 3D models are better predicting air-dried (low pressure) paper made from fibres of high rigidity. Geometric statistics of random networks explain some of the experimental observations. The statistical outputs of the 2D simulations were; network coverage (c), network thickness (τN), number of fibre crossings (NC) and the relative bonded area (RBA). In the case of 3D simulations, only τN was determined. The 2D and 3D outputs were measured for different fibre size distributions (Lf, D and ω).

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Energy reduction in pumping low consistency pulp fiber suspensions (2012)

Liquid transport is a vital segment of the economy. Pumping systems – whether used at a pulp and paper mill to transfer pulp stock, to pump petroleum through cross country pipeline or to transport tailings from a mine processing plant to a disposal site – are often one of the largest consumers of electrical energy. This thesis studies energy reduction in pumping low consistency fibre suspensions. The methods and procedures described in this work are applicable to any process where pumps are utilized. The main focus is on centrifugal pumps, the most commonly used pump at processing plants. Two methods are developed to achieve energy reduction: redesign of the original equipment manufacturer (OEM) impeller and pump performance monitoring via thermodynamic method.A novel methodology/process was developed for redesigning a more efficient impeller for existing pump installations. A computational fluid dynamics (CFD) process was developed for performance prediction of various impeller designs. The CFD process was validated using experimental pump loop results. Using OEM impeller geometry, design data and the redesign model, a series of eight optimal impellers were generated. The performances of these impellers were evaluated using the validated CFD process. The most efficient impeller design was selected for prototyping and experimental validation. A case study on Allis Chalmers PWO 6”x3”x14” pump showed that efficiency increase of 19.7% can be achieved with the redesign methodology.The validity of thermodynamic method was also studied in low consistency fibre suspension service. Head and efficiency curves for a low consistency pulp and paper centrifugal pump were measured for various low consistency pulp suspensions (0.5%, 1.0%, and 1.5%). These curves were simultaneously determined using two different approaches: conventional magnetic flow meter and differential pressure measurements; and by utilizing suction and discharge static pressure and temperature data (the thermodynamic method). It is found that addition of up to 1.5% mass fraction of softwood Kraft pulp to water did not affect the accuracy of the efficiency measurement when using the thermodynamic method. The pump efficiency calculated by thermodynamic method is consistent with the “gold standard” flow-meter-based method for flow rates within 90 – 115% of BEP (±1.0% maximum discrepancy).

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Multistage fibre length fractionation of softwood chemical pulp using a pressure screen equipped with smooth-holed screen cylinder (2012)

Often, fibre fractionation produce a higher value long-fibred reject stream and a lowervalue short-fibred accept stream simultaneously. Fractionation is only practical when amill can make use of all obtained fractions. This study sought to demonstrate thepotential of upgrading the reject fraction through multiple stages of fractionation whilecreating a new market for the remaining low value pulp for an efficient use of the rawmaterials.In this study, an NBSK pulp was fractionated on the basis of fibre length using a smallindustrial pressure screen Beloit MR-8 in multiple consecutive stages to isolate the lowvaluefines fraction from the feed pulp using the best combination of operatingparameters. The best conditions to carry out fractionation were determined by conductingexperiments to investigate the effect of varying volumetric reject ratio, Rv aperturevelocity, Vs aperture diameter and rotor tip speed, Vt on reject thickening and passageratio using several smooth-holed screen cylinders. This work shows that in general,increasing fines percentage in the accept and increasing fibre length in the reject wereobtained by using the screen cylinder with 0.5 mm apertures, the highest Rv at 0.6 and thesmallest Vs at 0.3 ms-¹.The strength properties of the unfractionated pulp were compared to the reject pulpproduced from the multistage fractionation. The tensile strength of the final reject pulp(which is 95 wt-% of the feed pulp) was increased up to 40% through the removal of onlya small amount of fines. The TEA, burst and tear indexes also improved. The Gurley airresistance was decreased up to 50%.The final accept fraction contains a significantly higher proportion of fines and it wasanalyzed by FPInnovations for its potential suitability as a raw material for a novel fibrebased product, Nanocrystalline Cellulose (NCC).

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Energy saving during pulp screening of A-PAM (2011)

No abstract available.

Pumping performance increase through the addition of turbulent drag-reducing polymers to pulp fibre suspensions (2010)

The addition of a small amount of long chain polymers to a turbulent fluid is known toreduce the wall shear stress and drag. Similarly, the addition of pulp fibres to aturbulent suspension is also turbulent-drag reducing despite pulp fibres having a lengthscale that is 1000 times larger than polymer molecules. The mechanism of dragreduction and its impact on centrifugal pump performance is poorly understood,especially when there is a combination of polymer and fibres in suspension.Centrifugal (slurry) pump performance was measured as a function of pulp fibre andPAM polymer concentration. Both the pump best efficiency and maximum head risewere greater when pumping modest concentrations of polymer solutions and lowconsistency pulp fibre than pure water. We measured an efficiency increase of 22percent and a maximum head increase of 4.3 percent with the addition of 150 ppm PAMpolymer over that of pure water. We measured an increase of 8 percent and 2.3percent in pump efficiency and maximum head coefficient, respectively, with 2 percentpulp fibres over that of water alone. With both 1 percent consistency pulp fibres and100 ppm of PAM polymers, we measured a 12 percent increase in efficiency over thatof pulp fibre alone. With both 2 percent consistency pulp fibres and 100 ppm of PAMpolymers present, we measure an 8 percent increase in efficiency over that of pulpsuspension alone. The reasons for the increased pump efficiency with addition ofadditives is not known but are thought to be due to the turbulent-drag-reducingproperties associated with flow of these suspensions.

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