The recovery and recycling of the spent chemicals from the kraft pulping process are economically and environmentally essential in an integrated kraft pulp and paper mill. The recovery process can be optimised by firing high-solids black liquor in the recovery boiler. Unfortunately, due to a corresponding increase in the liquor viscosity, in many mills, black liquor is fired at reduced solids concentration to avoid possible rheological problems. Online measurement, monitoring and control of the liquor viscosity are deemed essential for the recovery boiler optimization. However, in most mills, including those in New Zealand, black liquor viscosity is not routinely measured. Four batches of black liquors having solids concentrations ranging between 47 % and 70 % and different residual alkali (RA) contents were obtained from Carter Holt Harvey Pulp and Paper (CHHP&P), Kinleith mill, New Zealand. Weak black liquor samples were obtained by diluting the concentrated samples with deionised water. The viscosities of the samples at solids concentrations ranging from 0 to 70 % were measured using open-cup rotational viscometers at temperatures ranging from 0 to 115 oC and shear rates between 10 and 2000 s-1. The effect of post-pulping process, liquor heat treatment (LHT) on the liquors’ viscosities was investigated in an autoclave at a temperature >=180 oC for at least 15 mins. The samples exhibit both Newtonian and non-Newtonian behaviours depending on temperature and solids concentration; the onsets of these behaviours are liquor-dependent. In conformity with the literature data, at high solids concentrations (> 50 %) and low temperatures, they exhibit shear-thinning behaviour with or without thixotropy but the shear-thinning/thixotropic characteristics disappear at high temperatures (>= 80 oC). Generally, when the apparent viscosities of the liquors are <= ~1000 cP, the liquors show a Newtonian or a near-Newtonian behaviour. These findings demonstrate that New Zealand black liquors can be safely treated as Newtonian fluids under industrial conditions. Further observations show that at low solids concentrations (< 50 %), viscosity is fairly independent of the RA content; however at solids concentrations > 50 %, viscosity decreases with increasing RA content of the liquor. This shows that the RA content of black liquor can be manipulated to control the viscosity of high-solids black liquors. The LHT process had negligible effect on the low-solids liquor viscosity but led to a significant and permanent reduction of the high-solids liquor viscosity by a factor of at least 6. Therefore, the incorporation of a LHT process into an existing kraft recovery process can help to obtain the benefits of high-solids liquor firing without a concern for the attending rheological problems. A variety of the existing and proposed viscosity models using the traditional regression modelling tools and an artificial neural network (ANN) paradigm were obtained under different constraints. Hitherto, the existing models rely on the traditional regression tools and they were mostly applicable to limited ranges of process conditions. On the one hand, composition-dependent models were obtained as a direct function of solids concentration and temperature, or solids concentration, temperature and shear rate; the relationships between these variables and the liquor viscosity are straight forward. The ANN-based models developed in this work were found to be superior to the traditional models in terms of accuracy, generalization capability and their applicability to a wide range of process conditions. If the parameters of the resulting ANN models can be successfully correlated with the liquor composition, the models would be suitable for online application. Unfortunately, black liquor viscosity depends on its composition in a complex manner; the direct correlation of its model parameters with the liquor composition is not yet a straight forward issue. On the other hand, for the first time in the Australasia, the limitations of the composition-dependent models were addressed using centrifugal pump performance parameters, which are easy to measure online. A variety of centrifugal pump-based models were developed based on the estimated data obtained via the Hydraulic Institute viscosity correction method. This is opposed to the traditional approaches, which depend largely on actual experimental data that could be difficult and expensive to obtain. The resulting age-independent centrifugal pump-based model was implemented online as a black liquor viscosity soft sensor at the number 5 recovery boiler at the CHHP&P, Kinleith mill, New Zealand where its performance was evaluated. The results confirm its ability to effectively account for variations in the liquor composition. Furthermore, it was able to give robust viscosity estimates in the presence of the changing pump’s operating point. Therefore, it is concluded that this study opens a new and an effective way for kraft black liquor viscosity sensor development.

O licor negro, cuja composição majoritária é de lignina, é o principal subproduto gerado após a obtenção de polpa celulósica. Este polímero natural é caracterizado pela elevada massa molecular (MM) e composição aromática. Processos físico-químicos são empregados na fragmentação da lignina com o objetivo de obter compostos aromáticos, cuja fonte não renovável é oriunda de derivados do petróleo. A biodegradação da lignina, causada pela ação de enzimas ligninolíticas fúngicas pode prover compostos aromáticos de baixo peso molecular, como fenóis e antioxidantes, utilizados em diversos segmentos industriais. O objetivo deste trabalho foi estudar a modificação estrutural da lignina causada por fungos basidiomicetos coletados de mata nativa e campos de reflorestamento de eucalipto. Os ensaios de biodegradação foram inicialmente conduzidos utilizando-se 10 espécies de fungos, cultivados em duas concentrações de licor negro (10% e 15%, v/v). No ensaio com licor menos concentrado, utilizaram-se 10 espécies, e no ensaio com licor 15% utilizou-se somente a espécie Pycnoporus sanguineus. As análises realizadas para o estudo da modificação estrutural da lignina foram: espectroscopia na região do infravermelho (FTIR/ATR), cromatografia líquida de gel filtração e espalhamento de raios-X a baixo ângulo (SAXS). P. sanguineus e espécies de fungos do gênero Trametes possuem elevada capacidade de consumir a lignina presente no licor 10%, após 14 dias. A atividade de enzimas ligninolíticas de P. sanguineus foi investigada nas duas concentrações de licor. No licor 10%, observou-se elevada atividade das enzimas ligninolíticas manganês peroxidase (MnP), lacase e peroxidases; somente a MnP foi detectada com maior atividade no licor 15%. Análises de Demanda Bioquímica de Oxigênio (DBO) indicaram que o licor negro 10% biodegradado por P. sanguineus possui elevada carga de DBO, sendo tóxico a Daphia magna e Hydra attenuatta. Análises de metabólitos produzidos pelos fungos no licor negro 10% por cromatografia gasosa acoplada à espectrometria de massas (GC-MS) indicaram, principalmente, a produção de açúcares e álcoois em concentrações não muito diferentes dos seus respectivos controles. Embora os fungos sejam capazes de reduzir a massa molecular da lignina presente no licor negro, compostos derivados da sua fragmentação podem sofrer reações de condensação ou repolimerização, contribuindo, eventualmente, para elevar sua massa molecular / Black liquor which the bulk content is lignin, is the main product generated after obtaining cellulose pulp. This natural polymer is characterized by high molecular weight (MW) and aromatic compounds. Physical-chemical processes can be employed to fragment lignin and to produce aromatic compounds to replace those from non-renewable sources such as petroleum. Biodegradation of lignin can provide low molecular weight compounds, such as phenols and antioxidants, which may be employed in various industrial processes. The aim of this work was to investigate the structural modification of lignin caused by basidiomycetes fungi, obtained from native forest and Eucalyptus fields. The biodegradation assay was done with10 fungi species cultivated with two concentrations of black licor (10% and 15%, v/v). The assay with 10% liquor, 10 species of basidiomycete fungi were used, and in the assay with 15% liquor, it was used only Pycnoporus sanguineus. The analyses carried out to determine the structural modification of lignin were: infrared spectroscopy (FTIR/ATR), liquid chromatography gel filtration and small angle X-ray scattering (SAXS). P. sanguineus and fungi of Trametes genera had high capacity to consume the lignin content in the 10% liquor, after 14 days of cultivation. After that, P. sanguineus was selected for assays of ligninolytic enzymes activities in the two liquor concentrations. High activities of manganese peroxidase (MnP), laccase and peroxidase were detected in the 10% liquor, whereas in the concentration of 15% only high MnP activity was detected. Biochemical Oxygen Demand, analysis (BOD) indicated that the biodegraded liquor had high BOD load, and it was toxic to Daphia magna and Hydra attenuata. Metabolites produced by the fungi in the liquor 10% were analysed by gas chromatography-mass spectrometry (GC-MS), which indicated mainly the production of sugars and alcohols in concentrations not far from their respective controls. Although the fungus is able to decrease molecular weight of lignin, its fragments derivatives can undergo condensation or repolymerization reactions, contributing, eventually, to increase its molecular weight

This work focuses on high-temperature kraft black liquor gasification in the presence of H2O and CO2 in a laboratory-scale Laminar Entrained-Flow Reactor (LEFR). The effects of gasification conditions on hydroxide formation, carbon gasification rate, carbonate carbon and fixed carbon levels, alkali metal and sulfur species retention, and char yield were studied at atmospheric pressure and at 900-1000oC, and at residence times of 0.5-1.5 s. The results suggest that carbon gasification rates may be enhanced in the presence of H2O and CO2, with fixed carbon conversions of up to 95% at the earliest residence times at 1000oC. CO2 and H2O gasifying agents cause a significant increase in carbonate formation, with 22% of the initial carbon input forming carbonate as compared to 16% with one gasifying agent. Carbonate levels increase to a maximum level and then decrease at 900oC, but at 1000oC, carbonate decomposition processes are more dominant and cause lower levels of carbonate even at early residence times. The results show that alkali metal retention is high until vaporization occurs after 1.4 s at 900oC and at early residence times at 1000oC. Moreover, the results indicate that sulfur retention is an exothermic process, as sulfur capture increases with temperature. At 900oC, no hydroxide is produced until after 1.4 s, but at 1000oC, hydroxide appears to form readily even at the earliest residence times studied. The char product yields a maximum mole percent of 18-19% hydroxide, starting at intermediate residence times at 1000oC. Generally, hydroxide is not produced until fixed carbon conversions approach 95%. The results can be explained in terms of the interactions of phenolate and carboxylate catalytic moieties in the char product. The hydroxide formation results suggest that it may be possible to develop a gasification-causticization process that does not require external chemicals and would make the energy-efficient and environmentally friendly black liquor gasification technology an economic reality.

O licor negro, cuja composição majoritária é de lignina, é o principal subproduto gerado após a obtenção de polpa celulósica. Este polímero natural é caracterizado pela elevada massa molecular (MM) e composição aromática. Processos físico-químicos são empregados na fragmentação da lignina com o objetivo de obter compostos aromáticos, cuja fonte não renovável é oriunda de derivados do petróleo. A biodegradação da lignina, causada pela ação de enzimas ligninolíticas fúngicas pode prover compostos aromáticos de baixo peso molecular, como fenóis e antioxidantes, utilizados em diversos segmentos industriais. O objetivo deste trabalho foi estudar a modificação estrutural da lignina causada por fungos basidiomicetos coletados de mata nativa e campos de reflorestamento de eucalipto. Os ensaios de biodegradação foram inicialmente conduzidos utilizando-se 10 espécies de fungos, cultivados em duas concentrações de licor negro (10% e 15%, v/v). No ensaio com licor menos concentrado, utilizaram-se 10 espécies, e no ensaio com licor 15% utilizou-se somente a espécie Pycnoporus sanguineus. As análises realizadas para o estudo da modificação estrutural da lignina foram: espectroscopia na região do infravermelho (FTIR/ATR), cromatografia líquida de gel filtração e espalhamento de raios-X a baixo ângulo (SAXS). P. sanguineus e espécies de fungos do gênero Trametes possuem elevada capacidade de consumir a lignina presente no licor 10%, após 14 dias. A atividade de enzimas ligninolíticas de P. sanguineus foi investigada nas duas concentrações de licor. No licor 10%, observou-se elevada atividade das enzimas ligninolíticas manganês peroxidase (MnP), lacase e peroxidases; somente a MnP foi detectada com maior atividade no licor 15%. Análises de Demanda Bioquímica de Oxigênio (DBO) indicaram que o licor negro 10% biodegradado por P. sanguineus possui elevada carga de DBO, sendo tóxico a Daphia magna e Hydra attenuatta. Análises de metabólitos produzidos pelos fungos no licor negro 10% por cromatografia gasosa acoplada à espectrometria de massas (GC-MS) indicaram, principalmente, a produção de açúcares e álcoois em concentrações não muito diferentes dos seus respectivos controles. Embora os fungos sejam capazes de reduzir a massa molecular da lignina presente no licor negro, compostos derivados da sua fragmentação podem sofrer reações de condensação ou repolimerização, contribuindo, eventualmente, para elevar sua massa molecular / Black liquor which the bulk content is lignin, is the main product generated after obtaining cellulose pulp. This natural polymer is characterized by high molecular weight (MW) and aromatic compounds. Physical-chemical processes can be employed to fragment lignin and to produce aromatic compounds to replace those from non-renewable sources such as petroleum. Biodegradation of lignin can provide low molecular weight compounds, such as phenols and antioxidants, which may be employed in various industrial processes. The aim of this work was to investigate the structural modification of lignin caused by basidiomycetes fungi, obtained from native forest and Eucalyptus fields. The biodegradation assay was done with10 fungi species cultivated with two concentrations of black licor (10% and 15%, v/v). The assay with 10% liquor, 10 species of basidiomycete fungi were used, and in the assay with 15% liquor, it was used only Pycnoporus sanguineus. The analyses carried out to determine the structural modification of lignin were: infrared spectroscopy (FTIR/ATR), liquid chromatography gel filtration and small angle X-ray scattering (SAXS). P. sanguineus and fungi of Trametes genera had high capacity to consume the lignin content in the 10% liquor, after 14 days of cultivation. After that, P. sanguineus was selected for assays of ligninolytic enzymes activities in the two liquor concentrations. High activities of manganese peroxidase (MnP), laccase and peroxidase were detected in the 10% liquor, whereas in the concentration of 15% only high MnP activity was detected. Biochemical Oxygen Demand, analysis (BOD) indicated that the biodegraded liquor had high BOD load, and it was toxic to Daphia magna and Hydra attenuata. Metabolites produced by the fungi in the liquor 10% were analysed by gas chromatography-mass spectrometry (GC-MS), which indicated mainly the production of sugars and alcohols in concentrations not far from their respective controls. Although the fungus is able to decrease molecular weight of lignin, its fragments derivatives can undergo condensation or repolymerization reactions, contributing, eventually, to increase its molecular weight