Thesis (doctoral)--Helsinki University of Technology, 2000. / Includes bibliographical references. Also available on the World Wide Web.

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A laboratory investigation into foam separation processes, as applied to kraft pulping and bleaching effluents is described. Two methods, foam fractionation and ion flotation were tested in the laboratory. The procedures developed concentrated primarily on the removal of effluent colour because this property lent itself most readily to the available analytical methods, and because effluent colour removal presents one of the greatest waste water treatment problems facing the industry today. The foam fractionation technique was not successful. Substantial colour removals were obtained, but it was subsequently shown that the mechanism of removal was really an ion flotation. Positive results were obtained with the use of the ion flotation process for removal of effluent colour. At optimum conditions, the recovery of flotable material and the corresponding removal of effluent colour were in excess of 95 per cent. Variation of surfactant dosage showed that below a critical level no colour was removed. As concentrations increased above this value the amount of colour removed increased rapidly, reaching a high removal level beyond which increases in surfactant concentration were of little value. The rate of flotation recovery was found to be significantly affected by the air sparge rate and the sparger pore size, both parameters which would determine the area available for adsorption. The pH of the flotation cell solution had a marked effect on the system. Optimum pH was clearly defined as 5.1. Removal of material other than just the chromophoric fraction was apparent. Biological oxygen demand data, while not extensive, demonstrate a significant reduction in the bio-degradable portion of the effluent. The possible future development of the process into a viable candidate for industrial application is discussed. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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The use of black liquor gasification as an alternative to conventional chemical and energy recovery systems for spent liquors is an area of particular interest to the pulp and paper industry. The motivation to explore this technology is to improve the thermal efficiency of the recovery process by utilizing the energy content of the spent black liquor more effectively and provide chemical recovery for sodium and sulphur containing liquors for a local pulp and paper mill. A study of the available gasification technologies showed that the steam reforming process marketed by ThermoChem Recovery International is particularly suited to the mill in that it can handle a change to a sulphite pulping chemistry and also handle silica removal which is an inherent problem with the bagasse raw material that the mill uses. However the technology required further development and confirmation of process suitability before implementation at the mill. This aim of this project was to build and operate a gasifier based on the TRI concept to determine if this process is suitable for recovery of SASAQ black liquor from bagasse pulping. This included gaining an understanding of the process variables like the black liquor solids composition and the non-process element levels and required carrying out a mass balance on inorganic components across the reactor as well. The focus of this investigation was primarily on the front end of the project and entailed basic and detailed design of a pilot gasification unit. The pilot unit was subsequently constructed, commissioned and operated to prove the unit met the design intent. Preliminary results showing the conceptual proof of the technology are presented as well as performance tests showing the unit capability of gasifying a 3.1 1Ihr 60% solid content black liquor feed. Problematic areas that could influence the design of a scale-up unit were identified and highlighted for further development, with proposed solutions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

Combustion properties of kraft black liquor solids were studied using a laminar entrained flow reactor. The tendency of black liquors to release fume (compounds containing Na⁺, K⁺, Cl⁻, SO₄²⁻, SO₃²⁻, S₂0₃²⁻ and C0₃²⁻) during combustion were observed at 1000°C. Black liquor solids with a size fraction of 63 to 100 μm were burned in a mixture of 4% 0₂ and 96% N₂ at a residence time of 0.67 seconds. Combustion properties of one black liquor (liquor #3) were studied by varying the solids feed rate from 0.47 to 1.08 g/min (liquor feed rate study). Combustion properties of five North American and Finnish black liquors were studied at a target solids feed rate of 0.73 g/min (liquor to liquor study). Black liquor fuming was observed to be a decreasing function of solids feed rate and an increasing function of excess oxygen. The appearance of char residues varied from black and porous at high solids feed rates to white and dense at low solids feed rates. Combustion may have been enhanced at low solids feed rates by liquor swelling due to a combination of heat and mass transfer effects and limited at high solids feed rates by inter-particle and bulk gas mass transfer limitations. For the liquor to liquor study, black liquors were observed to release fume differently. Chars produced during this study varied in appearance, indicating that the black liquors had unique combustion properties. Variations in temperature and mass transfer effects resulting from liquor swelling properties were likely responsible for the variability in liquor fuming behavior. The liquors that contained the most NaCl and had the highest anionic equivalents as C0₃²⁻ (or other chemical species) produced the most fume. Sodium vaporization varied from 25.2% to 33.7%: Liquors #2 and #5 vaporized the most sodium and also had the lowest concentrations of measured anions in their char residues. Potassium and chloride enrichment factors for the five liquors were slightly lower than those of common industrial boilers. Liquor #3 had a concentration of Cl⁻ that was (roughly) an order of magnitude higher than the other liquors studied; however, it also had the lowest chloride enrichment factor. / Graduation date: 2002

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