Thesis (Ph.D.)--Washington State University. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1936. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MSc)--Stellenbosch University, 2005. / No english abstract available. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die effek van warm water uitloging van houtspaanders by hoë temperature en onder hoë druk voor alkaliese verpulping te ondersoek. Warm water uitloging van houtspaanders onder druk voor alkaliese verpulping was baie belowend, aangesien dit ekstrakstowwe verwyder het wat andersins verteringschemikalieë sou opgebruik het en ook verbertede verpulpingstoestande meegebring het. Gedurende uitloging het die houtstruktuur verander agv die verwydering van die ekstrakstowwe. Dit het veroorsaak dat die houtstruktuur meer toeganglik geword het, en dit het gelei tot 'n verbeterde diffusie van die kookloog. Die versnelde kookloogdiffusie het 'n verbeterde en meer gelykmatige delignifikasie meegebring. Warm water uitloging by verhoogde druk is ondersoek vir drie houtsoorte nl. Eucalyptus grandis, Acacia mearnsii en Pinus patuia. 'n Twee-uur en 'n een-uur uitlogingstyd van die houtspaanders voorafgaande Kraft en soda-AQ verpulping is ondersoek.Vergelyk met 'n een-uur uitloging is daar gevind dat die twee-uur uitloging van die houtspaanders te drasties was, met 'n gevolg van 'n vermindering in pulpopbrengs, vesellengte en pulpsterkte. Die verlaging III pulpsterkte kon toegeskryf word aan polisaggariedafbreking. Die een-uur uitloging het 'n hoër opbrengs opgelewer as beide die kontrole (nie uitgeloogde houspaanders) en die twee-uur uitgeloogde houtspaanders. Die een-uur uitlogingsperiode het besonder goeie verpulpingsresultate vir die ekstrakstofryke Acacia mearnsii houtspaanders getoon, met 'n bykomstige verbetering in pulpsterkte eienskappe.

The important role of black liquor in the pulp and paper industry has, been addressed and a review of conventional and potential alternative technologies has been made. Black liquor combustion properties and its combustion within a conventional recovery boiler, the principle of vortex combustion, and methods of computational fluid dynamics were summarized. In order to use the commercially available computational fluid dynamics package, PHOENICS, to simulate black liquor combustion in a vortex combustor, the black liquor combustion process was simplified and modelled and additional software programs were developed and attached to the commercial package. The developed module is capable of tracking trajectory paths of black liquor particles during combustion. A 250 kW vortex combustor was used for some experimental work. The combustor was first tested with natural gas and kerosene. The - combustion conditions were satisfied and their characteristics were presented. Atomization was the main technical problem in the combustion of black liquor. However, the environmental problem was also severe. The results were presented and discussed. Improvements of the system and further studied were suggested. Selection of a suitable turbulence model was made by comparing experimental data with the simulations from various turbulence models. Prandtl mixing length model gave closer predictions than k-? and k-1 model and therefore, it was used for the entire simulations. Simulations of natural gas combustion in a vortex combustor were made to establish skill and confidence in using the package, PHOENICS, to deal with combustion process. A series of black liquor combustion models were performed afterward using the particle tracking module developed. This led to the suggestion of a potential suitable geometry of a vortex combustor for black liquor incineration. The results were presented and discussed. Further simulation studies are also suggested.

In order to gain insights into ultrastructural changes taking place during the conversion of hardwoods into mechanical pulps, refiner pulp fibres were studied in detail using several microscopical techniques. Aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.) wood chips were used to produce thermomechanical (TMP), chemithermomechanical (CTMP) and chemimechanical (CMP) pulps. Following the hypothesis that there are fundamental differences in the surface and state of the fibres due to species and processing conditions, four pulps for each species and process were analyzed. Trends in fibre characteristic development were obtained within each group, based on the detailed optical analysis of 300 fibre cross-sections for each pulp. Fibre surface quality was the most important aspect of this study. Retention of middle lamella and of the layer, as well as the extent of exposure of the S₂ layer were evaluated. It was found that TMP processing of wood chips produced fibres with more exposure of the S₂ layer. Chemical pretreatment did not improve the extent of S₂ layer exposure nor the extent of fibrillation. However, the TMP fibres remained stiff, producing pulp sheets of low density and strength. Birch fibres showed a marked tendency to produce separation at or near the S₁/S₂ boundary. This resulted in high exposure of S₂ layers in TMP fibres, but produced a sheath of S₁ and ML around fibres from chemically-treated chips. This sheath was sometimes rolled back, exposing the fibre S₂ layer. Aspen TMP pulps showed high proportions of fibres with partially exposed S₂ layer. The application of chemical pretreatments to aspen chips resulted in fibres of similar levels of S₂ exposure than those achieved by TMP processing of this species, but only after reaching freeness levels of about 100 mL CSF. Fibres that showed radial failure were frequent in TMP but not in CTMP nor CMP pulps. The breakdown pattern of tension wood fibres (G-fibres) was also studied. TMP processing showed preferential breakdown of G-fibres, from which the G-layers were freed. This was not the case in the G-fibres from chemically-treated chips, in which the G-layer generally remained inside the fibres. Other categories discussed in the analysis of fibre cross sections included fibres with delamination of the S₂ layer and proportion of fibres distorted due to chemical impregnation. The breakdown of vessel elements (VE) was studied by comparing VE size frequency distributions and the proportion of whole VE that survived refining. TMP reduced VE into small fragments showing virtually no whole VE, while wood softening due to chemical pretreatment was responsible for a high proportion of whole VE in CTMP and CMP pulps. The VE from birch tend to be destroyed more easily than those from aspen, due to the intervessel pitting arrangement of the former. It is concluded that despite superior bonding potential of TMP fibres due to: - large S₂ exposure in fibres on account of separation at or near the S₁/S₂ boundary, - increased fibrillation, - longer fibrils in fines, and - release and exposure of highly cellulosic G-layers from tension wood in the case of aspen, the lack of conformability of TMP fibres, which translates into low sheet density, negates the promising benefits that otherwise would be obtained. / Forestry, Faculty of / Graduate

No description available.

No description available.

No description available.

No description available.

Environmental concerns and cost reduction have been the focus of pretreatment and extended delignification in Kraft pulping for some time now. Previous work has looked at the diffusion of tritiated water into softwood chips. This thesis looks at the diffusion of Na2S into southern pine softwood chips. Two size fractions were used. The measured diffusion data were compared to the equilibrium of mixing between the HS ion and water alone. Since pine is porous, effective diffusivities were calculated for each size fraction using a 1-dimensional model. Tortuosities were then calculated for the HS / pine wood system. These diffusivities are compared to values previously obtained for tritiated water.