This thesis was the report of the research done on the near-critical water gasification (NCWG) as an application for activated sludge treatment. The research started with the use of model compounds and binary mixtures of these compounds as feeds for the NCWG. High gasification yields were obtained using a commercial catalyst (Raney nickel), and it was found that interactions between model compounds in the binary mixtures resulted in lowering the gasification efficiencies. The research then shifted to the use of actual activated sludge samples and the search for novel catalysts for that application. Almost 70% of the sludge was gasified in the presence of the high amounts of Raney nickel. Hydrogen was the main product in the gas phase. However, Raney nickel lost half its activity after only 8 minutes of exposure to supercritical water. For some model compounds, novel catalysts formulated in our laboratories had better activities than the commercial ones. This was not the case for the NCWG of activated sludge.

The oxidation behavior of model binary and ternary alloys in supercritical water (SCW) was examined. Binary alloys contained 9 or 14 at% Cr. Ternary alloys had 1.5 at% of one of the following elements: Si, Al, V, Mn or Ti. Samples with different surface finishes were exposed to SCW for up to 500 hours. The oxidized samples were characterized using gravimetry, SEM, HRTEM and EDX. After exposure, a uniform double layer oxide with outwardly grown magnetite inwardly grown Fe-Cr mixed oxide was detected on most of samples. Alloys contains 14 at% Cr or/and 1.5 at% Si showed a mixed oxidation mode, where relatively thick double layer oxides coexisted with thin protective oxide. The coverage with the thin oxide increased with the increase of deformation and/or Cr and/or Si content. A 20 nm thick Si-enriched layer was detected at such alloy/oxide interfaces. This behavior is very similar to “third element effect”.

The oxidation behavior of model binary and ternary alloys in supercritical water (SCW) was examined. Binary alloys contained 9 or 14 at% Cr. Ternary alloys had 1.5 at% of one of the following elements: Si, Al, V, Mn or Ti. Samples with different surface finishes were exposed to SCW for up to 500 hours. The oxidized samples were characterized using gravimetry, SEM, HRTEM and EDX. After exposure, a uniform double layer oxide with outwardly grown magnetite inwardly grown Fe-Cr mixed oxide was detected on most of samples. Alloys contains 14 at% Cr or/and 1.5 at% Si showed a mixed oxidation mode, where relatively thick double layer oxides coexisted with thin protective oxide. The coverage with the thin oxide increased with the increase of deformation and/or Cr and/or Si content. A 20 nm thick Si-enriched layer was detected at such alloy/oxide interfaces. This behavior is very similar to “third element effect”.

Neste trabalho apresentamos alguns estudos teóricos sobre propriedades eletrônicas de sistemas atômicos e moleculares em fase líquida e ambiente supercrítico. A utilização dos fluidos supercríticos têm atraído muito interesse como meio solvente para propriedades moleculares, reações químicas e são vistos como alternativa aos solventes orgânicos t´óxidos. Assim como nos solventes convencionais, descrever suas propriedades por meio de estudos em n´nível molecular tem se tornado tão interessante quanto seu uso prático. Primeiramente realizamos o estudo da polarizabilidade estática do argônio e como esta propriedade se comporta em função da variação de pressão. Fizemos também um estudo deste sistema em torno do ponto crítico e região supercrítica. Dentro do intervalo de pressão que estudamos, não observamos variações significativas na polarizabilidade, embora no regime de baixas densidades este sistema apresentou certa dependência da polarizabilidade com a densidade. Neste estudo, também calculamos a constante dielétrica no ponto crítico. Em seguida estudamos o espectro de absorção do ´átomo de xenônio em ambiente formado por argônio líquido. Nesta parte, realizamos várias simulações com o objetivo de verificar o deslocamento da linha de absorção 5p 6s deste ´átomo em relação `a densidade, explorando também as condições supercríticas. Observamos que o deslocamento do espectro ocorrido em meio solvente é para maiores energias (blue shift) `a medida que a densidade aumenta, e obtemos bom acordo com os valores medidos. Por ultimo, realizamos um estudo da mudança de um espectro eletrônico molecular onde o solvente é a ´agua supercrítica. Utilizamos a molécula paranitroanilina como sonda solvatocromica, e observamos que mesmo no regime de alta temperatura e baixa densidade ainda ocorre a formação de ligações de hidrogênio entre soluto e solvente. Obtemos um red shift para a transição eletrônica em agua supercrítica. Este resultado é medido experimentalmente tanto para ´agua em condições ambiente como em condição supercrítica, mas em ´agua supercrítica o deslocamento ´e menor. Nosso resultado para a agua supercrítica está em bom acordo com o resultado experimental e mostra que a maior contribuição para este deslocamento ´e devido ao efeito das interações eletrostáticas. Porém, ao compararmos os resultados da ´agua em condições supercríticas com as condições normais de temperatura e pressão e o dióxido de carbono supercrítico como solventes, os resultados indicam que a aproximação de incluir apenas interações eletrostáticas ´e menos satisfatória e fornece somente parte do efeito de solvente. / In this work we present some theoretical studies of the electronic properties of atomic and molecular systems in liquid and supercritical environments. The study of supercritical fluids is a interesting topic in solvent effects on molecular properties and chemical reactions. Their use can be an alternative to organic toxic solvents. Describing their molecular solvent properties, as opposite to conventional solvents, has become important as of pratical use. First we study the static polarizability of atomic argon and its behavior with pressure. The critical and near critical points also were considered in this study. In the range of pressures used, it is not observed significant changes in the polarizability, although the system present some dependence with density in the supercritical region. We have then determined the dielectric constant at the critical point. Next we study the absorption electronic spectra of xenon atom in liquid argon environment. In this part, we performed several simulations with the aim of verifying the density dependence of the spectral shift of the 5p 6s line of xenon. The supercritical region was also explored. We obtain the spectral blue shift in solvent environment for increasing density in good agreement with experiments. Finally, we study the electronic spectra of a solvatochromic probe molecule, the paranitroaniline, in supercritical water and supercritical carbon dioxide. We observe that even for high temperature hydrogen bond persists between the solute and the water molecules. A red shift in the transition of the electronic spectra of paranitroaniline is well described. This red shift is observed experimentally in water, but in supercritical water it is less pronounced. Our results for supercritical water is in good agreement with the experimental result and show that the long-range electrostatic contribution dominates the solute-solvente interaction and gives the largest influence in the calculated spectrum. Water in normal conditions and supercritical carbon dioxide were also considered for comparison and the results indicates that including only the electrostatic contribution is less satisfactory and gives only part of the total solvent effect.

Orientador: Tânia Forster Carneiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-27T14:35:47Z (GMT). No. of bitstreams: 1 Lachos-Perez_Daniel_M.pdf: 2146698 bytes, checksum: bd9a09fc30626088c9dff682785f1200 (MD5) Previous issue date: 2015 / Resumo: Novas tecnologias de reaproveitamento de resíduos para a produção de novos produtos com gasto energético estão emergindo como uma forma eficiente e economicamente viável. Tecnologias utilizando água supercrítica podem representar uma alternativa ambientalmente correta, uma vez que promovem o desenvolvimento sustentável em relação aos métodos convencionais. Processos de hidrólise em água supercrítica dispensam solventes ácidos e processos de gaseificação em água supercrítica dispensam a secagem da amostra, ou seja, permitem o emprego de resíduos húmidos. Adicionalmente, processos de hidrólise e gaseificação utilizando fluidos supercríticos permitem um eficiente controle do processo através de pequenas variações nas condições de operação (pressão, temperatura, vazão, etc.). Trata-se de uma tecnologia em fase de desenvolvimento, existindo poucos relatos na literatura sobre sistemas de hidrólise e/ou gaseificação com água supercrítica e processos similares. A unidade piloto proposta neste trabalho permite o estudo dessa tecnologia e utilizando água supercrítica de forma a integrar em um mesmo equipamento dois processos: hidrólise seguida de gaseificação; proporcionando uma melhor relação custo-benefício associada a essas tecnologias. O sistema proposto tem aplicações no desenvolvimento de processos com água em condições sub e supercríticas de temperatura e pressão, buscando a obtenção de açúcares fermentáveis e/ou gases de interesse energético, tais como hidrogênio e metano. O objetivo principal deste trabalho foi projetar e construir um sistema em escala piloto capaz de realizar a conversão do bagaço da cana-de-açúcar em produtos de maior valor agregado, a partir de um reator de hidrólise operando em condições subcríticas de temperatura e pressão, seguido de um reator de gaseificação operando em condições supercríticas de temperatura e pressão, em regime semicontínuo. Testes preliminares foram realizados no reator de hidrólise com o objetivo de otimizar as condições de temperatura e pressão no primeiro reator previamente ao reator de gaseificação. Os resultados das cinéticas de hidrólise, com duração entre 15 e 25 minutos, indicaram altos valores de rendimento de açúcares redutores e redutores totais nas temperaturas de 200 e 250 ºC, independentemente dos valores de pressão estudados. Por outro lado à temperatura de hidrólise de 250 °C foi obtida maior rendimento de hidrólise, esse comportamento pode ser indicado devido a maior formação de açúcares observado neste experimento / Abstract: Waste recycling technologies to produce new products with energy recovery are emerging as efficient and economically viable alternative. Technologies using supercritical water can represent an environmentally friendly alternative, as they promote sustainable development compared to conventional methods. Hydrolysis processes in supercritical water do not require acid solvents and gasification processes in supercritical water dispense sample drying, or allow the use of wet waste. Additionally, hydrolysis and gasification processes using supercritical fluids allow an efficient control of the process by small variations in the operating conditions (pressure, temperature, flow rate, etc.). Since this is a technology under development, there are few reports in the literature on hydrolysis and / or gasification systems with supercritical water and similar processes. The pilot plant proposed in this work allows the study of supercritical water technology to integrating in one device two processes: the hydrolysis followed by gasification, providing a cost-benefit associated with these technologies. The proposed system has applications in process development with water in sub- and supercritical conditions of temperature and pressure to obtain fermentable sugars and / or gases such as hydrogen and methane. The main objective of this work was to design and to build a system at pilot plant scale capable of performing the conversion of sugar cane bagasse into higher added value products and energy, from a hydrolysis reactor operating in subcritical conditions of temperature and pressure followed by a gasification reactor operating in supercritical conditions of temperature and pressure, in a semi-batch system. Preliminary tests were carried out in the hydrolysis reactor in order to determine the optimal temperature and pressure conditions in the first reactor previous to gasification reactor. The results of the hydrolysis kinetics, lasting between 15-25 minutes showed high yield values of reducing sugars and total reducing sugars at the temperatures of 200 and 250 °C, independently of the pressure values studied. On the other hand, to the hydrolysis temperature of 250 ° C was obtained a yield higher hydrolysis, this behavior may be indicated due to larger formation of sugars observed in this experiment / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

In recent years, third-generation--or algae-based biofuels--have been studied extensively in order to reduce the risks of compromised food security, solve biofuel issues from past generations and supply continuous feedstock from energy crops. With the goal of a zero-carbon future, bioenergy with carbon capture and storage (BECCS) is a technology that extends to multiple areas--including algae-based biofuels that avoid greenhouse emissions from biomass processing. Algae are aquatic plants or microorganisms, classified as micro and macroalgae; they are of considerable scientific interest because they are fast-growing, with a photosynthetic metabolism that generates carbon sources from atmospheric CO$_2$. Macroalgae (seaweed) can be cultivated in aquaculture farms and collected through mechanical devices; the macroalga selected for this study is Macrocystis pyrifera, a giant brown seaweed characterized by its size and its carbon and oxygen-rich composition. Conventional methods for thermal conversion into potential fuels, such as biomass carbonization, pyrolysis, and gasification are not efficient for biomass with high moisture. For this reason, the research community has introduced new methods like hydrothermal carbonization, liquefaction, and gasification. This project focuses on the process simulation in Aspen plus® V12 to produce green hydrogen from macroalgae biomass by pyrolysis, gasification, and hydrothermal gasification. Hydrogen production was maximized through sensitivity analysis, achieving a hydrogen yield of 2.08% in hydrothermal gasification, 2.06% for pyrolysis, and 1.85% for gasification.

No description available.

Experimental data on SuperCritical-Water (SCW) cooled bundles are very limited. Major problems with performing such experiments are: 1) small number of operating SCW experimental setups and 2) difficulties in testing and experimental costs at very high pressures, temperatures and heat fluxes. However, SuperCritical Water-cooled nuclear Reactor (SCWRs) designs cannot be finalized without such data. Therefore, as a preliminary approach experiments in SCW-cooled bare tubes and in bundles cooled with SC modeling fluids can be used. One of the SC modeling fluids typically used is Freon-12 (R-12) where the critical pressure is 4.136 MPa and the critical temperature is 111.97ºC. These conditions correspond to a critical pressure of 22.064 MPa and critical temperature of 373.95ºC in water. A set of experimental data obtained in a Freon-12 cooled vertical bare bundle at the Institute of Physics and Power Engineering (IPPE, Obninsk, Russia) was analyzed. This set consisted of 20 cases of a vertically oriented 7-element bundle installed in a hexagonal flow channel. To secure the bundle in the flow channel 3 thin spacers were used. The dataset was obtained at equivalent parameters of the proposed SCWR concepts. Data was collected at pressures of about 4.65 MPa for several different combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. Heat fluxes ranged from 9 kW/m2 to 120 kW/m2 and mass fluxes ranged from 440 kg/m2s to 1320 kg/m2s. Also inlet temperatures ranged from 70ºC – 120ºC. The test section consisted of fuel elements that were 9.5 mm in diameter with the total heated length of 1 m. Bulk-fluid and wall temperature profiles were recorded using a combination of 8 different thermocouples.The data was analyzed with respect to its temperature profile and heat transfer coefficient along the heated length of the test section. In a previous study it was confirmed that there is the existence of three distinct regimes for forced convention with supercritical fluids. (1) Normal heat transfer; (2) Deteriorated heat transfer, characterized by higher than expected temperatures; and (3) Improved heat transfer, characterized by lower than expected temperatures. All three regions were observed for the 7 rod bundle experiments. This work compares the experimental data to predictions based upon current 1-D correlations for heat transfer in supercritical fluids. Results show that no current 1-D correlation was able to accurately predict heat transfer coefficients within ±50%. A parametric analysis of the data was also completed to determine if continuity in the experiment was present. Results of this study show that two distinct regions are present in the data. For cases with a mass flux below 1200 kg/m2s wall temperature profiles appear to be normal while in cases with mass flux above 1200 kg/m2s temperature given by the wall thermocouples were higher than normal. This phenomenon occurred regardless of heat flux-to-mass flux ratios. / UOIT

In working towards a sustainable society, recycling and recovery of products together with handling of scarce resources must be considered. The growing quantities of sludge from wastewater treatment plants and the increasingly stringent restrictions on landfilling and on agricultural use of sludge are promoting other disposal alternatives. Sludge fractionation, providing sludge volume reduction, product recovery and separation of toxic substances into a small stream, has gained particular interest. In this thesis, the potential for phosphate release and recovery from treated sewage sludge is investigated as an alternative for agricultural use in urban areas. Leaching and recovery experiments were performed on sludge residue from supercritical water oxidation, ash from incineration and dried sludge at different temperatures. Results showed that acid or alkaline leaching is a promising method to release phosphate from sewage sludge treated with supercritical water oxidation, incineration, or drying at 300°C. The leaching is affected by a number of factors, including how the sludge residue has been produced, the origin of the sludge residue, the quantity of chemicals added and the presence of ions in the leachate. The implementation of any particular sludge treatment technology would depend on cost, environmental regulations, and social aspects. The results of this thesis may be beneficial for minimizing the use and cost of chemicals, and give increased knowledge for further development of technology for phosphate recovery. / QC 20100930

CANDU (CANada Deuterium Uranium) reactor utilizes Pressure Tube (PT) fuel channel design and heavy water as a coolant. Fuel channel annulus gas acts as an insulator to minimize heat losses from the coolant to the moderator. Since fuel bundles are continuously under high neutron fluxes, annulus gas nuclides undergo different nuclear transformations generating new composition of the gas that might have different physical properties which are undesirable for the annulus system. In addition, gas nuclides become radioactive and lead to an increase of the radioactive material inventory in the reactor and consequently to an increase of radiation levels. Pressure Tube Reactor (PTR) and Pressure Tube Supercritical Water Reactor (PT SCWR) fuel channel models have been developed in Monte Carlo N-Particle (MCNP) code. Neutron fluxes in the fuel channel annulus gas have been obtained by simulating different types of neutron sources in both PTR and PT SCWR fuel channels. Transmutation rates of annulus gases have been calculated for different gases (CO2, N2, Ar and Kr) at different pressures and temperatures in both fuel channels. The variation of the transmutation rates, neutron fluxes and gas densities in the annulus gas have been investigated in PTR and PT SCWR fuel channels at constant pressures and different temperatures. MCNP code along with NIST REFPROP [14] and other software tools have been used to conduct the calculations. / UOIT