Physical property data was used to test two hypotheses pertaining to the impact of a chemical pre-treatment on the qualities of low consistency refined pulp. The first objective was to determine whether the addition of a chemical treatment would effectively accelerate the refining process when compared to a regular pulp. This involved the measurement of the physical property data and how it changed with increased refining energy. The second objective was to determine how the chemical treatment affected fibre development during refining, and whether its implementation could result in enhancement of inter-fibre bondability. Theoretical models for the physical properties of paper were used to study the fibre-to-fibre bonding properties of the tested paper samples. Additionally, SEM images were obtained to study the deferences in morphology of the tested pulp samples.

Physical property data was used to test two hypotheses pertaining to the impact of a chemical pre-treatment on the qualities of low consistency refined pulp. The first objective was to determine whether the addition of a chemical treatment would effectively accelerate the refining process when compared to a regular pulp. This involved the measurement of the physical property data and how it changed with increased refining energy. The second objective was to determine how the chemical treatment affected fibre development during refining, and whether its implementation could result in enhancement of inter-fibre bondability. Theoretical models for the physical properties of paper were used to study the fibre-to-fibre bonding properties of the tested paper samples. Additionally, SEM images were obtained to study the deferences in morphology of the tested pulp samples.

A crucial parameter in the production of mechanical pulp through refining is energy consumption. Although low consistency (LC) refining has been shown to be more energy efficient than conventional high consistency refining, the degradation of mechanical properties of the end-product paper due to fiber cutting has limited the widespread adoption of LC refining. In conventional control strategies, the onset of fiber cutting is determined by post-refining measurement of pulp properties which does not enable rapid in-process adjustment of refiner operation in response to the onset of fiber cutting. In this dissertation, we exploit a piezoelectric force sensor to detect the onset of fiber cutting in real time. Detection of the onset of fiber cutting is potentially beneficial in low consistency refining as part of a control system to reduce fiber cutting and increase energy efficiency. The sensor has a probe which replaces a short length of a refiner bar, enabling measurement of normal and shear forces applied to pulp fibers by the refiner bars. The custom-designed sensors are installed in an AIKAWA pilot-scale 16-in. single-disc refiner at the Pulp and Paper Centre at the University of British Columbia. Trials were run using different pulp furnishes and refiner plate patterns at differing rotational speeds and a wide range of plate gaps. Pulp samples were collected at regular intervals and the pulp and paper properties were measured. We observe distinct transitions in the parameters that characterize the distributions of peak normal and shear forces which consistently correspond to the onset of fiber cutting. In addition, the analysis of the power spectrum of the sensor data shows that the magnitude of the dominant frequency can be used as an indicator of fiber cutting. The power of the time domain signal of the normal force is shown to be the most reliable and consistent indication of the onset of fiber cutting. This parameter consistently identifies the onset of fiber cutting, as determined by fiber length data, for all tested pulp furnishes and plate patterns. In addition, we investigate the effect of pulp furnish and plate pattern on bar forces in LC refining. For tested pulp furnishes and at all plate gaps, the plate with higher bar edge length (which has smaller bar width and groove width) results in lower mean peak normal and shear forces but higher mean coefficient of friction. Moreover, at the onset of fiber cutting, the mean peak normal force of softwood pulp is higher than that for hardwood pulp. Our results also show that the mean coefficient of friction at the onset of fiber cutting is a function of plate gap, pulp furnish, and plate pattern. / Graduate / 2019-01-09

The thesis is focussed on low consistency (LC) refining of mechanical pulp. Theresearch included evaluations of energy efficiency, development of pulpproperties, the influence of fibre concentration on LC refining and effects of rotorposition in a two-zoned LC refiner. Trials were made in mill scale in a modern TMP line equipped with an MSDImpressafiner for chip pre-treatment, double disc (DD) first stage refining and aprototype 72-inch TwinFlo LC refiner in the second stage. Tensile index increasedby 8 Nm/g and fibre length was reduced by 10 % in LC refining at 140 kWh/adtgross specific refining energy and specific edge load 1.0 J/m. Specific lightscattering coefficient did not develop significantly over the LC refiner. The above mentioned TMP line was compared with a two stage single disc highconsistency Twin 60 refiner line. The purpose was to evaluate specific energyconsumption and pulp properties. The two different process solutions were testedin mill scale, running similar Norway spruce wood supply. At the same tensileindex and freeness, the specific energy consumption was 400 kWh/adt lower in theDD-LC concept compared with the SD-SD system. Pulp characteristics of the tworefining concepts were compared at tensile index 47 Nm/g. Fibre length was lowerafter DD-LC refining than after SD-SD refining. Specific light scattering coefficientwas higher and shive content much lower for DD-LC pulp. The effects of sulphite chip pre-treatment on second stage LC refining were alsoevaluated. No apparent differences in fibre properties after LC refining werenoticed between treated and untreated pulps. Sulphite chip pre-treatment iniiicombination with LC refining in second stage, yielded a pulp without screeningand reject refining with tensile index and shives content that were similar to nonpre-treated final pulp after screening and reject refining. A pilot scale study was performed to investigate the influence of fibreconcentration on pulp properties in LC refining of mechanical pulps. MarketCTMP was utilised in all trials and fibre concentrations were controlled by meansof adjustments of the pulp consistency and by screen fractionation of the pulp. Inaddition, various refiner parameters were studied, such as no-load, gap and baredge length. Pulp with the highest fibre concentration supported a larger refinergap than pulp with low fibre concentration at a given gross power input. Fibreshortening was lower and tensile index increase was higher for long fibre enrichedpulp. The results from this study support the interesting concept of combiningmain line LC refining and screening, where screen reject is recycled to the LCrefiner inlet. It has been observed that the rotor in two-zoned refiners is not always centred,even though pulp flow rate is equal in both refining zones. This leads to unequalplate gaps, which renders unevenly refined pulp. Trials were performed in millscale, using the 72-inch TwinFlo, to investigate differences in pulp properties androtor positions by means of altering the pressure difference between the refiningzones. In order to produce homogenous pulp, it was found that uneven plate gapscan be compensated for in LC refiners with dual refining zones. Results from thedifferent flow rate adjustments indicated that the control setting with similar plategap gave the most homogenous pulp.

Reducing energy consumption in pulp and paper refining requires a deep understanding of all the processes involved. This dissertation investigates fundamental mechanics of the low consistency mechanical refining process. Three studies investigate forces applied to wood fibers with the focus on how force profiles during bar passing events change with process variables such as fiber length and refiner load. In the first study a high resolution rotary encoder and a piezo ceramic force sensor are implemented in a 16-inch laboratory-scale low consistency refiner to explore the effect of plate gaps on bar-force profiles. The rotary encoder data is used to locate the rotor bars relative to the stator bar in which the sensor is located. Force profiles for bar passing events are registered to the position of rotor bars relative to the stator bar in which the sensor is located and mean force profiles are produced. These mean force profiles have potential to shed light on the fundamental mechanisms of mechanical refining. For large gaps, there is a late peak in the force profiles that occurs toward the end of the bar passing event. For gaps that are less than the critical gap, below which fiber cutting occurs, there is an early peak in the force profiles that occurs at the start of the bar passing event. It is hypothesized that the early peak represents the corner force and, therefore, that corner force is causal in the onset of fiber cutting. In the second study a set of piezo ceramic force sensors is implemented in a 52-inch mill-scale low consistency refiner to explore the effect of varying operating conditions on bar force profiles. Force profiles for individual bar passing events are identified based on key features in the time domain force data based on the knowledge acquired from the previous study in the pilot-scale refiner. The individual bar force profiles are classified as single peak events which feature one peak corresponding to the fiber compression force and as dual peak events corresponding to fiber compression force and the corner force. It is shown that dual peak events which are considered to represent the corner force, are present throughout the whole range of refining and increase with increased refining energy. After applying the dual peak analysis to the data from the previous study this behaviour was also found in the pilot-scale refiner data. Furthermore, it is found that different radial positions on the stator plate are subjected to different force profiles. This is thought to be due to the difference in tangential speed and a change in the fiber and floc material properties at different radial positions. In the third study the effect of refiner plate wear on bar force sensor measurements is explored by applying the dual peak analysis to long term data acquired from the mill-scale refiner. Bar passing events are analysed based on the dual peak ratio and the timing of the early peak in the dual peak events. Force measurements are evaluated over the full run time of a set of refiner plates. When comparing force profiles with refiner plate wear measurements and discharge fiber analysis, it is found that the decrease in the prevalence of the corner force correlates with the wear of the leading edge of the refiner bars, or bar rounding, for the run time of the refiner plate. This is accompanied by a decrease in plate performance which is represented by a decrease in fiber length and freeness reduction for the same refiner load. / Graduate