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    Alkaline pulping : deadload reduction studies in chemical recovery system
    (Georgia Institute of Technology, 2004-12-02) Chandra, Yusup
    The kraft pulping process has been known for decades. The focus in kraft pulping has always been on better operation of the chemical recovery system. One of the targets is on deadload (sodium sulfate (Na2SO4) and sodium carbonate (Na2CO3)) reduction in white liquor. A model based on several literature references was developed to study the effect of deadload reduction. A base model was developed based on current mill operation. This base model was compared to the deadload reduction model. Overall improvement, such as operating cost saving and revenue generation was achieved from deadload reduction. Operating cost saving involves less deadload chemical in chemical recovery system, and less water that was associated with the deadload itself. Revenue generation involves generating more steam and heat from the recovery boiler that can be used for mill purposes or energy revenue. Two important variables to achieve deadload reduction are causticizing efficiency and reduction efficiency.
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    Kinetics of the Titanate Causticization Reactions in a Potassium-Based Process
    (Georgia Institute of Technology, 2004-04-16) Ho, Luis Holing
    The objective of this study was to model the kinetics of direct causticization of potassium-based chemical using titanium dioxide, TiO₂. The starting materials were K₂CO₃ and TiO₂. Potassium chemical was used because there is an indication that potassium carbonate, K₂CO₃, might offer benefits over sodium carbonate, Na₂CO₃, such as the elimination of potassium build-up in sodium-based pulping. Experiments were run at six different temperatures. Half were below potassium carbonate’s melting point while the other half were above. Reaction rates and conversions increased with temperature, and the maximum conversion achieved was 0.90. Several kinetic models were fitted to the data. Valensi-Carter showed a good fit for the solid-solid reaction, while ash diffusion control model was chosen to describe the solid-liquid reaction with TiO₂ stayed in solid phase. The samples from the heated experiments were then leached with water to produce KOH. The amount of KOH was found to increase with temperature. It implied that more 4K₂O•5TiO₂ was produced at higher temperatures. Reacting K₂CO₃ with K₂O•3TiO₂ might interest industry more because TiO₂ is added to the recovery system as a make up only. The models used did not show good fits for the whole conversions; therefore, additional study should be done to develop a model that could describe low conversions as well as high conversions.
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    Determination of Reaction Kinetics of Barium Sulfide with Sodium Carbonate and Sodium Sulfate to Reduce Deadload in the Recovery Cycle
    (Georgia Institute of Technology, 2004-04-15) Branham, Joshua M.
    The following study deals with the characteristics of the reaction to form BaSO₄ and BaCO₃ from Na₂SO₄ and Na₂CO₃, respectively, using BaS as the other reactant. These reactions would theoretically increase the efficiency of the chemical recovery process in papermaking to near 100% by completely converting Na₂SO₄ to Na₂S and Na₂CO₃ to NaOH. Kinetic data were collected, and it was determined that both reactions were overall first order with rate constants of 0.037s⁻¹ for the formation of BaSO₄ and 0.021s⁻¹ for the formation of BaCO₃. Also, it was found that both reactions go to completion in under three minutes. The heats of reaction were studied and found to be negligible. BaSO₄ particle sizes averaged approximately 4.5μm and remained steady with respect to time while BaCO₃ particle sizes were approximately 21μm initially, but decreased over the course of several days. BaCO₃ formed agglomerates which began to break down immediately, but BaSO₄ did not form agglomerates at all. No explanation for why BaCO3 formed agglomerates and BaSO₄ did not could be determined experimentally or found in the literature. Attempts to increase the particle size of BaSO₄ included seeding the initial solution with BaSO₄ crystals and increasing the concentration of reactants from 0.100M solutions each to 0.292M for BaS and 1.31M for the sodium salts. Both seeding and increased reactant concentration had no effect on particle size. The settling rates of BaSO₄ and BaCO₃ particles were also studied. BaSO₄ exhibited mainly discrete and some flocculant settling characteristics, and the suspension as a whole settled quickly with some smaller particles remaining in suspension for a lengthy period of time. Hindered and mainly compression settling occurred with BaCO₃ because of the agglomerates that formed due to strong particle-particle interactions. BaCO₃ settled slowly, but virtually no particles remained in suspension after the bulk of the particles settled.