Roberto Cesar de Oliveira Romano

Permeability optimization and performance evaluation of hot aerosol filters made using foam incorporated alumina suspension

Porous ceramic samples were prepared from aqueous foam incorporated alumina suspension for application as hot aerosol filtering membrane. The procedure for establishment of membrane features required to maintain a desired flow condition was theoretically described and experimental work was designed to prepare ceramic membranes to meet the predicted criteria. Two best membranes, thus prepared, were selected for permeability tests up to 700 degrees C and their total and fractional collection efficiencies were experimentally evaluated. Reasonably good performance was achieved at room temperature, while at 700 degrees C, increased permeability was obtained with significant reduction in collection efficiency, which was explained by a combination of thermal expansion of the structure and changes in the gas properties.

Otimização da permeabilidade de filtros de aerossóis para altas temperaturas preparados a partir da técnica de adição de espuma aquosa em suspensão cerâmica

Este trabalho e parte de um projeto de desenvolvimento de filtros cerâmicos para a remocao de material particulado disperso em correntes gasosas em temperaturas elevadas. Os filtros cerâmicos utilizados para esta finalidade devem apresentar elevada porosidade aliada a uma distribuicao homogenea de poros interconectados, resultando em estrutura permeavel e com boa resistencia mecânica e eficiencia de coleta. Uma rota de processamento recentemente desenvolvida e utilizada para o processamento das pecas, ja que permite a obtencao de todas as caracteristicas requeridas para uma filtracao eficiente. Nesta tecnica, os materiais porosos sao processados a partir da incorporacao de espumas aquosas em uma suspensao cerâmica de alumina e consolidados a partir da adicao de cimento aluminoso. Comparado com outras rotas de processamento, este processo e mais atrativo, pois permite a fabricacao de pecas com geometrias complexas, economicamente viaveis e sem utilizacao de aditivos toxicos. O objetivo deste trabalho foi otimizar a composicao cerâmica de modo a atender aos requisitos de permeabilidade do filtro, tendo como base sua operacao economica em temperaturas elevadas em processos como incineracao de residuos, producao de cimento ou queima de biomassa em caldeiras em plantas quimicas.

Influence of the dispersion process in the silica fume properties

Silica fume (SF) has been widely used in cement based products, as it promotes a better packing and increases its mechanical strength, either by its pozzolanic activity, and/or by the filler effect promoted by its fine particle size distribution. However, in order to achieve these benefits, the SF must be dispersed in the suspension, exposing completely its reactive surface and improving particle packing. As a by-product of metallic silicon production, SF particles are strongly bonded as a consequence of densification process involved during its generation, resulting in macroscopic agglomerated grains that require high energy for an effective dispersion. Then, the present study reports the SF dispersion in deionized water under low and high shear conditions, imposed by using a conventional laboratory suspension mixer and a high energy in-line mixer, respectively.

Hydration of Portland cement with red mud as mineral addition

The use of red mud from Bayer process in association with Portland cement has been shown to be promising because of its good performance on the hardened state. However, the physicochemical interactions during the cement reaction have not been explored in depth in the literature. As the red mud is rich in iron, aluminates, silicate and, mainly, sodium components, the interaction with Portland cement is rather complex. Additionally, the large amount of finer particles can introduce another variable in the development of hydrated compounds. This work was aimed at evaluating the impact from partial substitution of Portland cement for different contents of red mud collected in an alumina production plant in the northeast of Brazil. The hydration reaction was monitored by isothermal conduction calorimetry and the setting time of cement by the Vicat test. The results indicate that the residue of bauxite ore affects the chemical reaction of cement, due to nucleation effects, packing and dilution, and the high amount of sodium and soluble aluminates from the red mud causes the formation of sodium silicoaluminate hydrate (NASH) and a greater amount of hydrated calcium aluminate, which had no effect on the setting time.

Caracterização reológica de suspensões cimentícias mistas com cales ou filitos

Filitos sao tipos de rochas metamorficas que vem sendo utilizados ultimamente como insumos em composicoes de argamassa de revestimento, em substituicao a cal. A melhora da trabalhabilidade e da plasticidade dos materiais cimenticios, principais motivos para a utilizacao das cales, sao as caracteristicas obtidas tambem com a utilizacao dos filitos. Este trabalho tem como objetivo avaliar as caracteristicas de suspensoes cimenticias formuladas com cal ou filito, a partir de ensaios de reometria rotacional para a avaliacao das propriedades das suspensoes durante o fluxo, e oscilatoria para a avaliacao da cinetica de consolidacao. Os resultados mostraram que, apesar de as caracteristicas fisicas, quimicas e mineralogicas dos pos serem muito diferentes, as cales hidratadas do tipo I (CHI) nao se diferenciaram dos filitos durante o fluxo, mas durante o endurecimento foram observadas consideraveis alteracoes na cinetica de aglomeracao.

Efeito da calcinação do resíduo de bauxita nas características reológicas e no estado endurecido de suspensões com cimento Portland

Este estudo ilustra o impacto da calcinacao de residuo de bauxita (RB) nas propriedades de suspensoes formuladas com cimento Portland, tanto no estado fresco como no endurecido. As suspensoes foram avaliadas contendo uma razao constante de agua-cimento e teor de residuo variando de 5% a 20% em peso e em substituicao ao cimento. As propriedades reologicas e a resistencia mecânica foram alteradas em funcao do aumento do teor de RB, mas a calcinacao nao teve influencia no resultado final obtido, seja no estado fresco ou no endurecido. Assim, pode-se afirmar que a utilizacao de residuo de bauxita, natural ou calcinada, em formulacoes com cimento Portland pode reduzir o consumo de cimento, sendo uma alternativa para a utilizacao de uma grande quantidade deste tipo de residuo.

Permeability characterization of hot aerosol filters prepared with foaming of ceramic suspensions

This work is part of a project to develop ceramic filters to treat flue gases from cement plants, biomass boilers and waste incinerators. Ceramic filters used for these purposes must present high porosity, homogeneous porous distribution (interconnected) to result in bodies with high mechanical strength, permeability and collection efficiency for fine particles. A method recently developed has been used for the filters processing. In this new processing route, the porous samples were prepared through the incorporation of aqueous foams into alumina-based suspensions. Compared to other techniques, this process seems to be an attractive and cost effective solution for fabricating complex shaped bodies, without toxic admixtures. The procedure to establish the required features of the filtering membrane for a desired flow condition is described, as well as the experimental work to produce and select the ceramic membranes with such requirements.

Torque Measurement in Real Time during Mixing and Kneading of Bread Dough with High Content of Resistant Maize Starch and Enzymes

Abstract In this work, a methodology to measure torque during dough mixing in large scale was developed and the baking performance of bread dough formulated with resistant starch (RS) and enzymes was evaluated. Dough was formulated with 12.5 g/100 g of RS and 4 mg/100 g of a mixture of enzymes, glucose-oxidase (Gox), tranglutaminase (TG) and xylanase (HE) in proportions according to a three-component mixture design of experiments. Dough was mixed in a large-scale dynamic rheometer measuring instant torque and speed in real time through a personal computer (PC) interface. Maximum torque during mixing and parameters of the dough development curves obtained from rheofermentometer were fit to mathematical models within 95 % of confidence. Gox and TG showed positive effects on the maximum height of dough, while HE showed a negative one. Also, it was found that Gox and TG in the presence of HE could be important for reducing dough weakening.

Acompanhamento da hidratação de cimento Portland simples com resíduo de bauxita

A substituicao parcial de cimento Portland por residuo de bauxita (RB) resulta em produtos com, no minimo, propriedades similares as dos produtos fabricados com o ligante puro. No entanto, as interacoes fisico-quimicas entre os diferentes tipos de cimento e o RB durante a reacao de hidratacao ainda e pouco explorada em literatura. A elevada quantidade de sodio e a presenca de Al2O3, SiO2 e Fe2O3 sao fatores que afetam a formacao dos produtos hidratados e dependem do tipo de cimento utilizado na mistura. Sendo assim, este trabalho foi realizado com o objetivo de avaliar o impacto da presenca do residuo de bauxita em associacao ao cimento Portland simples nas primeiras idades de hidratacao. Calorimetria de conducao isotermica, difracao de raios X, analise termogravimetrica e espectroscopia de infravermelho foram as tecnicas escolhidas para o monitoramento. Os resultados ilustraram que a presenca do residuo coletado na planta da Alcoa (Pocos de Caldas) aumenta o tempo de inducao, o consumo de portlandita, e as quantidades de etringita e monossulfoaluminato formadas. Ao mesmo tempo, houve formacao de silicoaluminato de sodio e bicarbonato de sodio, devido as reacoes com silicatos, aluminatos e com o carbonato do cimento.

Consolidação de pastas cimentícias contendo policarboxilatos um estudo calorimétrico e reológico

Polycarboxylates are frequently used as additives to concrete production in the construction industry. The additive increases the dispersion of the particles, reduces the amount of water, and improves the mechanical properties of concrete in the fresh and settled state. However, although it is well known that polycarboxylate additives enable the production of high performance concretes, their presence may affect on both kinetics and thermodynamics of cements particles during hydration reaction through consolidation. While the flow of heat released by the hydration reaction can be measured by isothermal calorimetry, concrete consolidation can be measured by oscillatory rheometry. The results obtained separately, when considered together could better illustrate the effect of the additives on the cement setting. This was the main subject in this work. Therefore, cement pastes containing commercial CPIIE-32 were evaluated by simultaneous heat of hydration and rheological measurements with different amounts of polycarboxylate. The results obtained separately, when considered together can better illustrate the effect of additive content during the hardening, and this approach is presented as a main objective of this work. For this, cement pastes formulated with CPII-32 were evaluated according to the variation of the content of polycarboxylate and the results showed that the rate of consolidation(promoted by the joint action of the chemical reaction and particle agglomeration)has direct relation with the level of the additive.