Made available in DSpace on 2015-03-26T14:01:02Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2835217 bytes, checksum: b3fc87e9e63a523c32790c1de91c6b8a (MD5) Previous issue date: 2010-06-14 / Most of the Kraft pulp produced in the world come from continuous digesters. Digester corrosion has become a significant topic for the pulp and paper industry since it brought about the need for high expenditures with repairs, replacement of components and upgrade of materials, as well as losses in connection with unplanned outages. Risks to life and property are also significant, as catastrophic failure of pressure bearing equipment may also result. From the Eighties to present days, corrosion problems in many pulp and paper mills around the world have been increasing, for reasons ranging from materials and design aspects of the digesters themselves, to process modifications introduced ever since. The present work examines this scenario, studies the corrosive behavior of continuous digesters in its several forms, and seeks to indicate the main causes. Actual corrosion cases are presented and the main current protective technologies are discussed. Electrochemical testing, metallurgical analyses, corrosivity testing and field inspections are used to support the discussions and conclusions. Highlight is given to the field experience with a type 316 stainless-clad digester, the only known continuous cooker built in such material in the industry, whose prospective corrosion hazards prompted the execution of studies and protective measures that are unique for stainless cooking vessels. The risks to carbon or austenitic stainless steel digesters running on modern cooking processes are demonstrated to be significant. The effectiveness of the main protective technologies, as well as the compatibility among them, was proved. The need to include these technologies in cooking plant retrofit projects was established. / A maior parte da celulose Kraft produzida no mundo provém de digestores contínuos. A corrosão destes digestores tornou-se uma questão relevante para a indústria de celulose, na medida em que trouxe a necessidade de elevados gastos com reparos, substituições de componentes e melhoria de materiais, bem como prejuízos por paralisações imprevistas e prolongadas da produção. O risco ao patrimônio e à vida humana é também considerável, já que há possibilidade real de falhas catastróficas em equipamentos pressurizados. Desde a década de 80 até os dias atuais, os problemas de corrosão em digestores de muitas fábricas de celulose Kraft vêm se acentuando, por razões que vão desde materiais e aspectos construtivos dos próprios digestores até mudanças nos processos desde então introduzidas. O presente trabalho examina este cenário, estuda o comportamento corrosivo dos digestores contínuos em suas diversas formas e procura evidenciar as principais causas. Casos reais de corrosão e proteção são apresentados e as principais tecnologias protetoras atualmente disponíveis são discutidas. Testes eletroquímicos, análises metalúrgicas, testes de corrosividade e inspeções de campo são utilizados para suportar as discussões e conclusões. Destaca-se a experiência com um digestor revestido em aço inoxidável tipo 316,sem similar conhecido, cujos riscos potenciais de corrosão instaram a execução de estudos e a adoção de providências inéditas para digestores em material inoxidável. Os riscos de corrosão dos digestores em aço carbono ou inoxidável austenítico operando com processos atuais são evidenciados como sendo significativos. A eficácia das principais tecnologias protetoras, bem como a compatibilidade entre elas, foi comprovada. A necessidade de inclusão destas tecnologias em projetos de retrofit de cozimento foi estabelecida.

A escassez das fontes de fósforo e o alto consumo de energia associado à produção de fertilizantes nitrogenados serão problemas que deverão ser enfrentados no futuro. A recuperação de nutrientes das águas residuárias na forma de estruvita tem sido considerada como uma alternativa para atenuar estes problemas. Na América Latina, a produção de estruvita a partir de esgoto ainda não é uma tecnologia bem conhecida e, portanto, a finalidade deste trabalho é contribuir com uma melhor compreensão dos fenômenos envolvidos. Para isso, a pesquisa foi dividida em três etapas: 1) produção de estruvita a partir de efluente de reator anaeróbio de fluxo ascendente com manto de lodo (RAFA); 2) produção de estruvita a partir de sobrenadante de digestor anaeróbio de lodo de um processo com remoção biológica de fósforo (DALRBF) e 3) influência do cálcio na estruvita produzida na etapa 2. Nas três etapas, ajustaram-se as concentrações de magnésio, a fim de obter razões fósforo:magnésio (P:Mg) pré-estabelecidas, e o pH entre 8,00 e 10,50. Os resultados da primeira etapa mostraram que não foi possível produzir estruvita no efluente do RAFA nas condições testadas. No entanto, foram observadas remoções de fósforo e de nitrogênio, devido à formação de fosfatos de cálcio e de magnésio amorfos. Os resultados da segunda etapa comprovaram a viabilidade de produção de estruvita de sobrenadante de DALRBF e mostraram que os consumos molares dos íons fosfato (PO43-), amônio (NH4+) e magnésio (Mg2+) ou as remoções destes (%) não devem ser os únicos parâmetros para avaliar a formação de estruvita, pois outros compostos cristalizam ou precipitam e reduzem a qualidade do mineral. Para um meio com condições semelhantes às testadas nesta etapa, uma razão P:Mg 1:2 e um pH igual a 9,50 asseguram a máxima recuperação de nutrientes como estruvita com concentração mínima de impurezas, facilitando seu posterior uso como fertilizante. Os resultados da terceira etapa mostraram que uma fase amorfa de fosfato de cálcio ou de magnésio se forma na superfície da estruvita. / The shortage of the phosphorus sources and high-energy consumption associated to the nitrogen fertilizers production will be problems in the future. The nutrient recovery from wastewater as struvite has been considered as an alternative to alleviate these problems. In Latin America, production of struvite from wastewater is not yet a wellknown technology and therefore the purpose of this work is to contribute to a better understanding of the phenomena involved. This research work was performed in three phases: 1) production of struvite from upflow anaerobic sludge blanket reactor effluent; 2) production of struvite from anaerobic digester supernatant of enhanced biological phosphorus removal process (ADS-EBPR) and 3) influence of calcium in the struvite produced in the phase 2. In three phases, the magnesium concentrations were adjusted to obtain the preset phosphorus:magnesium (P:Mg) ratios and the pH was adjusted between 8,00 and 10,50. The results of the first phase showed that it is not possible to produce struvite in the upflow anaerobic sludge blanket reactor effluent in the tested conditions. However, removal of nitrogen and phosphorus was observed because amorphous calcium and magnesium phosphates were produced. The results of the second phase showed that it is possible to produce struvite in the ADS-EBPR and the molar consumptions of phosphate (PO43-), ammonia (NH4+) and magnesium (Mg2+) or removals (%) should not be the only parameters to evaluate the struvite formation, because other compounds crystallize or precipitate and reduce the quality of the mineral. In the similar conditions tested in this phase, a P:Mg ratio 1:2 and pH 9,50 assure maximum nutrients recovery as struvite with minimum impurities concentration, facilitating its subsequent use as fertilizer. The results of the third phase showed that amorphous calcium or magnesium phosphates were produced on the struvite surface.

A escassez das fontes de fósforo e o alto consumo de energia associado à produção de fertilizantes nitrogenados serão problemas que deverão ser enfrentados no futuro. A recuperação de nutrientes das águas residuárias na forma de estruvita tem sido considerada como uma alternativa para atenuar estes problemas. Na América Latina, a produção de estruvita a partir de esgoto ainda não é uma tecnologia bem conhecida e, portanto, a finalidade deste trabalho é contribuir com uma melhor compreensão dos fenômenos envolvidos. Para isso, a pesquisa foi dividida em três etapas: 1) produção de estruvita a partir de efluente de reator anaeróbio de fluxo ascendente com manto de lodo (RAFA); 2) produção de estruvita a partir de sobrenadante de digestor anaeróbio de lodo de um processo com remoção biológica de fósforo (DALRBF) e 3) influência do cálcio na estruvita produzida na etapa 2. Nas três etapas, ajustaram-se as concentrações de magnésio, a fim de obter razões fósforo:magnésio (P:Mg) pré-estabelecidas, e o pH entre 8,00 e 10,50. Os resultados da primeira etapa mostraram que não foi possível produzir estruvita no efluente do RAFA nas condições testadas. No entanto, foram observadas remoções de fósforo e de nitrogênio, devido à formação de fosfatos de cálcio e de magnésio amorfos. Os resultados da segunda etapa comprovaram a viabilidade de produção de estruvita de sobrenadante de DALRBF e mostraram que os consumos molares dos íons fosfato (PO43-), amônio (NH4+) e magnésio (Mg2+) ou as remoções destes (%) não devem ser os únicos parâmetros para avaliar a formação de estruvita, pois outros compostos cristalizam ou precipitam e reduzem a qualidade do mineral. Para um meio com condições semelhantes às testadas nesta etapa, uma razão P:Mg 1:2 e um pH igual a 9,50 asseguram a máxima recuperação de nutrientes como estruvita com concentração mínima de impurezas, facilitando seu posterior uso como fertilizante. Os resultados da terceira etapa mostraram que uma fase amorfa de fosfato de cálcio ou de magnésio se forma na superfície da estruvita. / The shortage of the phosphorus sources and high-energy consumption associated to the nitrogen fertilizers production will be problems in the future. The nutrient recovery from wastewater as struvite has been considered as an alternative to alleviate these problems. In Latin America, production of struvite from wastewater is not yet a wellknown technology and therefore the purpose of this work is to contribute to a better understanding of the phenomena involved. This research work was performed in three phases: 1) production of struvite from upflow anaerobic sludge blanket reactor effluent; 2) production of struvite from anaerobic digester supernatant of enhanced biological phosphorus removal process (ADS-EBPR) and 3) influence of calcium in the struvite produced in the phase 2. In three phases, the magnesium concentrations were adjusted to obtain the preset phosphorus:magnesium (P:Mg) ratios and the pH was adjusted between 8,00 and 10,50. The results of the first phase showed that it is not possible to produce struvite in the upflow anaerobic sludge blanket reactor effluent in the tested conditions. However, removal of nitrogen and phosphorus was observed because amorphous calcium and magnesium phosphates were produced. The results of the second phase showed that it is possible to produce struvite in the ADS-EBPR and the molar consumptions of phosphate (PO43-), ammonia (NH4+) and magnesium (Mg2+) or removals (%) should not be the only parameters to evaluate the struvite formation, because other compounds crystallize or precipitate and reduce the quality of the mineral. In the similar conditions tested in this phase, a P:Mg ratio 1:2 and pH 9,50 assure maximum nutrients recovery as struvite with minimum impurities concentration, facilitating its subsequent use as fertilizer. The results of the third phase showed that amorphous calcium or magnesium phosphates were produced on the struvite surface.

PhD (Geography) / Department of Geography and Geo-Information Sciences / Improved access to modern affordable, sustainable and reliable energy supply is fundamental in the development of any economy and in the achievement of sustainable development goals. However, energy as a resource is increasingly and becoming scare in many countries and subsequently expensive, with a substantial impact on the socio-economic progress, especially in any country that lacks the financial, physical, social and human capital to secure its energy supply. Energy can also be produced though the anaerobic fermentation of biological waste, such as animal excrement, which is methane-rich. Fermentation also produces a nutrient-rich digestate. Biogas can be used for domestic purposes, such as cooking and heating. Furthermore, it can be converted into electricity. Biogas technology is of particular significance in rural households, where energy crisis are common. This thesis therefore aimed at developing an adoption and sustainable utilisation framework of biogas as an alternative source of energy for greenhouse gases emission reduction in the Limpopo Province. The sample involved 72 households with biogas digesters, which were purposively sampled and 128 households without digesters, which were randomly selected. The study was based on the primary data that were elicited using open and closed-ended questionnaires. Empirically, the results of this thesis developed a sustainable, simplified, appropriate and comprehensive framework for biogas adoption and utilisation, including an analysis of important factors that could influence the adoption of this desired technology, for cost-effectiveness and sustainability. / NRF

No description available.

AD is regarded as a sustainable technology that could assist the UK Government meet internationally agreed GHG emission targets by 2050. However, the mature status of the technology is based on expensive systems that rely on high energy feedstock to be profitable. Meanwhile, the natural biodegradation of cow slurry is a recognised contributor to climate change despite having a relatively low CH4 potential because of the large volumes produced. Economic mixing is essential to the cost-effectiveness of farm AD but techniques applied are not always appropriate as slurry is a shear thinning thixotropic Herschel-Bulkley fluid and therefore challenging to mix. The apparent viscosity of slurry and the shear stress induced was most influenced by solids content (exponential change) followed by temperature (linear). Most shear thinning occurred before a rising shear rate of 20s-1 was achieved with the fluid acting near-Newtonian above. Thixotropic recovery occurred within 1 hour of resting. Rheological values were also much higher than previously reported. Highest CH4 production occurred in the first 10 days of the batch process using a range of mixing regimes with different shear rates and rest periods. During fed-batch operations, changing shear rate had a minimal effect on CH4 production using a 30-day HRT whereas shorter rest periods increased production. Specific CH4 production rate was highest when feeding and mixing coincided. However, when HRT was reduced (OLR increased) the CH4 produced by all mixed regimes significantly increased with highest values being achieved using high intensity mixing rested for short periods. Lower HRTs also requires smaller digesters. Parasitic mixing energy invariably had the most influence on net energy production. Signs of instability were evident after 20 days using the low HRT. Significant microbial adaptation was also observed as the experiments progressed. The research outcomes demonstrate that mixing regime and HRT can be managed to maximise net energy production whilst reducing capital expenditure.

MENVSC / Department of Ecology and Resource Management