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The drainage- and dewatering-controlling mechanisms in a screw press were detailed in this work. Three pulps (kraft pulp, bleached chemi-thermomechanical pulp, and thermomechanical pulp) were studied to compare a wide range of wood fibre types. The dewatering was controlled by the screw press parameters and the pulps’ properties. Filtration was found to be the controlling mechanism in the first part of the screw press for the three pulps, and it was less important when the fines content was greater. In the compression zone, the degree of compression was affected by the pulp flexibility and the fibres’ tendency to entangle. Filtrate flow rate monitoring along the screw press could be a good indicator of where the transition from filtration to consolidation occurs. The pressure along the screw press did not change much in the filtration zone, and it notably increased near the discharge end. When the drainage was very high, the pulp feed increased, causing the pulp axial velocity in the end part to be greater than the screw’s linear advance.

A Thune SP23 screw press dewatering parameters were studied. The dewatering efficiency was affected more by the rotational speed and the pulp properties. The counter-pressure affects dewatering near the discharge end, and it was observed to influence the outlet consistency and filtrate flow rate of Kraft, which has much longer fibres and fewer fines compared to TMP and BCTMP. The feed stock freeness and consistency are very important variables to consider in the screw press performance. The freeness reflects the degree of drainage, which is an important parameter to consider when optimising the screw press, while the feed consistency is a parameter of the fibre-fibre contact degree. The pulp properties, especially the fines content and fibre flexibility are also two very important parameters that affect the screw press performance. This study was to provide an insight of the screw press performance and to show the complex effect of the operational parameters on the dewatering characteristics. Using three different pulps, Kraft and TMP softwood fibres and a BCTMP hardwood fibres, we have shown that the fines content and fibre properties are two dominant properties that should be highly considered when operating a screw press.

TEMPO-oxidized thermomechanical pulp (TMP) prepared at low-oxidized and highly oxidized levels was compared with untreated TMP to observe the advantage of each pulp on paper properties. While the low oxidized pulp and non-oxidized pulp gave similar properties, highly oxidized TMP significantly increased tensile strength and decreased tear strength. Brightness was negatively affected by oxidation. In order to improve the paper optical properties, the use of a conventional mineral filler retention system was studied, using clay as filler. The high charge induced by the oxidized pulp significantly modified the pulp retention behavior. Moreover, paper made from pulp containing oxidized pulp and clay presented considerably better tensile strength with a loss in tear resistance for the same brightness target, which could be interesting for some paper applications.

The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation was mainly studied in laboratory scale and needs to be scaled-up for any future industrial implantation. With this objective, the...

4-Acetamido-TEMPO-mediated oxidation was carried out on thermomechanical pulp (TMP) to further investigate the extraction components of the oxidized pulp. Successive extractions on non-oxidized, bleached and oxidized TMP have shown that components were easier to extract from the oxidized pulp. The pulp lignin content demonstrated that the highest content of lignin was removed by sodium hydroxide extraction. Moreover, more than two times the amount lignin was extracted from oxidized pulp compared to non-oxidized pulp. The measured carboxylic groups showed that the highest amounts of the oxidized components were removed after the first extraction. However, after each extraction, reduced but still significant amounts of carboxylic groups were present in the extracted material. Thermogravimetric analysis showed that 4-acetamido-TEMPO oxidation treatment induced a decrease in the fibre degradation temperature caused by a weakening in the fibre structure. The results also demonstrated that some components of the highly oxidized pulp were more easily dissolved because of the critical extraction conditions. Furthermore, the recovered precipitate in the extraction solvent had different XPS characteristics according to the initial pulp treatment. The analysis of the oxidized TMP precipitate showed that the precipitate from hot water extraction was the most highly oxidized, while the precipitate from sodium hydroxide extraction approached pure lignin characteristics.

The aim of this study was to evaluate the performance of selective refining combined with ozone inter-stage treatment in a TMP process. A fractionation process was carried out to separate the primary pulp into two fractions, a long-fibre fraction and a short-fibre fraction. Different charges of ozone, namely 1%, 1.5%, and 2%, were used to treat the long-fibre fraction, and only the treated pulp went to the second refining stage. Finally, the secondary pulp was recombined with the primary short-fibre fraction to be compared to a control TMP trial. Results showed that 21% of the total refining energy can be saved when 1.5% ozone inter-stage treatment is applied before selective refining compared with whole pulp refining, when the pulp freeness is 100 mL. At this level of ozone charge, a slight increase in tensile strength is observed with no significant variation in tear index.

The principal objective of this research was to study the morphological changes of Jack pine (Pinus banksiana) earlywood (EW) and latewood (LW) in thermomechanical pulping (TMP). The results indica...

The optimization of complex processes usually involves many competing objectives; in this case there is typically no solution that yields optimal values for all of the objective criteria and the decision-maker must therefore find a reasonable compromise. In recent years, new multicriteria methods have been developed to assist the practitioner in achieving a judicious compromise among the various competing objectives. One method, the rough set method (RSM), is able to encapsulate the preferences of an expert within a simple set of logical rules that are used to rank a large number of feasible solutions according to these preferences. The RSM was used in this investigation to determine the optimal operating region of a high yield pulping process. This pulping process has seven input variables that can be manipulated to optimize four objective criteria characterizing the product: brightness, specific refining energy, extractive content, and rupture length. Results show that an optimal solution zone can be easily defined and zones of decreasing preference can be drawn. This information is very useful to the practitioner for choosing the desired operating conditions and for analyzing the robustness of the preferred operating scenarios from a process control point of view.

For many decades, the utilization of jack pine in the pulp and paper industry has attracted considerable interest but without any major breakthrough. However, in the past few years the emergence of new technologies has provided hope for its potential use. One of these technologies consists in the addition of hydrogen peroxide within the thermomechanical pulping process. To study the influence of numerous process parameters on the interstage treatment of jack pine and to optimize this complex process, a D-optimal experimental design was conducted. A total of 7 variables were considered. It was found that to maximize the properties of the fibres and the resulting paper, a temperature of 115°C with a narrow plate gap at the first refining stage and a high consistency at the second stage had to prevail. A sodium hydroxide treatment radically improved the fibre bonding properties without affecting the tear strength but at the expense of a loss of 4,6 points in ISO brightness. Validation trials allow to draw some conclusions on the advantages and shortcomings of this type of experimental design. This design is efficient, provided sufficient information is available to target likely interactions. Otherwise, a screening design would be required thus increasing the total cost of the study. L'utilisation du pin gris dans l'industrie des pâtes et papiers suscite un grand intert depuis de nombreuses decennies. Ces dernieres annees, l'emergence de nouvelles technologies apporte un regain d'espoir pour le futur. Une de ces technologies consiste a utiliser du peroxyde d'hydrogene lors du procede de mise en pâte thermomecanique. Un plan d'essais D-Optimal a ete utilise pour etudier l'influence de plusieurs parametres de ce procede. Ce type de plan d'experimentation permet de traiter un nombre important de variables simultanement tout en requerant peu d'essais, meme lorsque 7 variables sont mises en cause. Pour le pin gris, l'utilisation d'une temperature de 115°C accompagnee d'un faible entrefer lors du premier stade de raffinage ainsi que d'une consistance elevee au deuxieme stade, permet de developper au maximum les proprietes des fibres et du papier produit. Un traitement intermediaire a la soude augmente radicalement les proprietes de liaison interfibres sans affecter l'indice de dechirure mais fait, par ailleurs, chuter la blancheur de 4,6 points. Des essais de confirmation permettent de discuter des lacunes et des avantages de ce type de plan d'essais. Ce plan est efficace a la condition de connaitre assez le procede pour pouvoir cibler les interactions d'interet. Sinon, un plan de tri serait necessaire, ce qui augmenterait le co-t global de l'etude.

A series of pilot scale refining trials has been conducted to study the impact of refining conditions on the energy efficiency of the process and on the handsheet quality of a chemimechanical pulp. Black spruce (Picea mariana) chips, cooked to a yield of 90% and a sulphonate content of 1.4%, were refined in two atmospheric stages. Plate gap and consistency in each stage was controlled according to a central composite design. Statistical models of refiner performance were constructed from these experimental results and a non-linear optimization of process conditions was conducted. Optimization results were verified with plant trials which indicate that increasing the ratio of specific energy applied in the first stage leads to a reduction of approximately 15% in the total energy required. Inversely, this strategy can be used to obtain significant increases in pulp quality for a given energy input. The results also indicate that the largest proportion of energy must be applied to the fibres at high consistency. On a effectue une serie d'essais de raffinage a l'echelle pilote afin d'etudier l'impact des conditions de raffinage sur l'efficacite energetique du procede et sur la qualite de la feuille de papier d'une pâirc;te chimico-mecanique. Des copeau d'epinette noire (Picea mariana), cuits pour un rendement de 90% et une teneur en sulphonate de 1,4% ont ete raffines dans deux etages atmospheriques. L'intervalle entre les plateaux et la consistence ont ete controles pour chaque etage a l'aide d'une plan composite centre. On a construit des modeles statistiques de performance des raffineurs a partir de ces resultats experimentaux et on a realise une optimisation non lineaire des conditions de procede. Les resultats de l'optimisation ont ete verifies par des essais en usine qui indiquent qu'une augmentation du taux d'energie specifique dans le premier etage entraiine une reduction d'approximativement 15% de l'energie totale requise. Inversement, cette strategie peut servir a obtenir des augmentations significatives de la qualite de la pâte pour un apport d'energie donnee. Les resultats indiquent egalement que la plus forte proportion d'energie doit etre appliquee aux fibres a consistance elevee.