A Pease-Anthony Venturi scrubber is a gas cleaning device that uses liquid, injected in the equipment as jets, to remove contaminants from the gas. The liquid jet is atomized into droplets, which are dispersed throughout the equipment due to the turbulence. The performance of the scrubber is affected by the spatial distribution of the droplets. Although CFD models have been used to predict the droplet dispersion, these models are expensive. Alternatively, the concept of "jet spreading angle" could be used as a simple and quick way to estimate droplet dispersion. The purpose of this paper is to measure the spreading angle of jets transversally injected into the throat of a Venturi scrubber and correlate it with both gas and jet velocities. The throat gas velocities varied between 59 and 74 m/s and the jet velocity between 3.18 and 19.1 m/s. The angles were measured through image analysis, obtained with high velocity photography. The spreading angle was found to be strongly dependent on jet velocity.

Este trabalho é parte de um projeto de desenvolvimento de filtros cerâmicos para a remoção de material particulado disperso em correntes gasosas em temperaturas elevadas. Os filtros cerâmicos utilizados para esta finalidade devem apresentar elevada porosidade aliada a uma distribuição homogênea de poros interconectados, resultando em estrutura permeável e com boa resistência mecânica e eficiência de coleta. Uma rota de processamento recentemente desenvolvida é utilizada para o processamento das peças, já que permite a obtenção de todas as características requeridas para uma filtração eficiente. Nesta técnica, os materiais porosos são processados a partir da incorporação de espumas aquosas em uma suspensão cerâmica de alumina e consolidados a partir da adição de cimento aluminoso. Comparado com outras rotas de processamento, este processo é mais atrativo, pois permite a fabricação de peças com geometrias complexas, economicamente viáveis e sem utilização de aditivos tóxicos. O objetivo deste trabalho foi otimizar a composição cerâmica de modo a atender aos requisitos de permeabilidade do filtro, tendo como base sua operação econômica em temperaturas elevadas em processos como incineração de resíduos, produção de cimento ou queima de biomassa em caldeiras em plantas químicas.

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.

Neste trabalho, filtros com estrutura fibrosa foram produzidos utilizando-se matéria-prima de baixo custo, disponível comercialmente e caracterizados para aplicações em filtração de aerossóis. Mantas refratárias sílico-aluminosas comerciais foram prensadas uniaxialmente, utilizando-se 10% em massa de acetato de polivinila como ligante. Nesta etapa, as amostras foram submetidas à compactação com diferentes pressões para obtenção de diferentes porosidades. Após a prensagem, as amostras foram submetidas a um tratamento térmico a 500 ºC durante 1 h para a degradação do polímero. Subseqüentemente, as amostras foram sinterizadas a 1200 ºC durante 1 h, resultando em uma estrutura fibrilar porosa, composta por mulita (3SiO2.2Al2O3), com porosidade na faixa de 50 a 75%. A morfologia dos filtros fibrosos foi caracterizada através de microscopia eletrônica de varredura, que revelou uma estrutura tridimensional porosa de fibras interconectadas. A resistência mecânica foi avaliada através de ensaios de compressão e de flexão em quatro pontos. Ensaios de permeabilidade e eficiência de coleta de partículas com diferentes diâmetros foram efetuados e os resultados comparados a filtros comerciais. Os valores obtidos para a permeabilidade e eficiência de coleta estão na ordem de grandeza esperada para filtros de gases, apresentando assim grande potencial para aplicações industriais.

Filters with fibrous structure were produced from low cost, commercially available raw materials and characterized for aerosol filtration. Refractory aluminosilicate fibers were uniaxially pressed with polyvinyl acetate as binder. Different pressures were applied, which yielded samples with different porosities. After pressing, the samples were heat treated at 500 ºC during 1 h in air for debinding with subsequent sintering at 1200 ºC for 1 h, which resulted in porous fibrous structures composed mainly by mullite (3SiO2.2Al2O3) with porosity in the range of 50%-75%. The microstructure of the fibrous filters was evaluated by scanning electron microscopy, which revealed a porous morphology comprised by three-dimensional interconnected fibers. Mechanical strength was measured by compressive and 4-point bending tests. Permeability and particle collection efficiency were evaluated and compared with commercially available filters. The permeability and collection efficiency values are in the order of magnitude of cellular supports for aerosol filters and, therefore, suitable for several technological applications.

Este trabalho é parte de um projeto de desenvolvimento de filtros cerâmicos para a remoção de material particulado disperso em correntes gasosas em temperaturas elevadas. Os filtros cerâmicos utilizados para esta finalidade devem apresentar elevada porosidade aliada a uma distribuição homogênea de poros interconectados, resultando em estrutura permeável e com boa resistência mecânica e eficiência de coleta. Uma rota de processamento recentemente desenvolvida é utilizada para o processamento das peças, já que permite a obtenção de todas as características requeridas para uma filtração eficiente. Nesta técnica, os materiais porosos são processados a partir da incorporação de espumas aquosas em uma suspensão cerâmica de alumina e consolidados a partir da adição de cimento aluminoso. Comparado com outras rotas de processamento, este processo é mais atrativo, pois permite a fabricação de peças com geometrias complexas, economicamente viáveis e sem utilização de aditivos tóxicos. O objetivo deste trabalho foi otimizar a composição cerâmica de modo a atender aos requisitos de permeabilidade do filtro, tendo como base sua operação econômica em temperaturas elevadas em processos como incineração de resíduos, produção de cimento ou queima de biomassa em caldeiras em plantas químicas.

This work is part of a Brazilian 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.

The collection efficiency of a laboratory scale plate-wire electrostatic precipitator, operating in the removal of airborne PM2.5, was carried out. The variables investigated were the applied potential (V), the gas velocity (v o), the diameter of the discharge electrodes (2rSE), the distance between electrodes (2c) and of the total precipitator length (L NE). The test particles were high grade alumina with median diameter of 0.6 micrometers and maximum diameter of 2.5 micrometers. The results showed, qualitatively, a good agreement with the theory of electrostatic precipitation. Quantitatively, the results were compared to predictions from two existing correlations from the literature and both underestimated the precipitator overall efficiency when using the assumption of pseudo-homogeneous electrical field strength. The predictions improved significantly when the field strength was calculated with the equation proposed by Kihm et al. (1985, 1987) and included a homogeneous space charge, as proposed by Riehle (1997).

An investigation was conducted on influence of removal time on the particle substrate adhesive force. The centrifuge technique was used to determine the adhesion force at different compression and removal rates. A microcentrifuge with a maximum rotation of 14000 rpm was used to both compress upon particles and remove them from the surface of the substrate. An image analysis program (Image-Pro Plus 4.5) was employed to monitor the number of particles adhering to and removed from the surface of the substrate after each increase in angular speed. The influence of removal time on the adhesion force was investigated, using removal times of 1, 3 and 5 minutes, which indicated that removal time does not interfere with the adhesion force within the diameter range analyzed here.

This work gives sequence to the study on the measurement of the electrostatic charges in aerosols. The particle charge classifier developed for this purpose and presented in the previous paper (Marra and Coury, 2000) has been used here to measure the particle charge distribution of a number of different aerosols. The charges acquired by the particles were naturally derived from the aerosol generation procedure itself. Two types of aerosol generators were used: the vibrating orifice generator and turntable Venturi plate generator. In the vibrating orifice generator, mono-dispersed particles were generated by a solution of water/ethanol/methylene blue, while in the rotating plate generator, six different materials were utilized. The results showed no clear dependence between electric charge and particle diameter for the mono-dispersed aerosol. However, for the poly-dispersed aerosols, a linear dependence between particle size and charge could be noticed.

Neste trabalho foram utilizados filtros cerâmicos para filtração de aerossóis, constituídos por dupla camada, onde a primeira camada é formada por um suporte celular de elevada porosidade com diâmetro de poro controlado e a segunda formada por uma película filtrante. A camada suporte foi obtida pela técnica de replicação cerâmica de espuma poliuretânica, por meio da impregnação de uma suspensão aquosa de Al2O3. Foram utilizados suportes de 45 e 75 poros/polegada. A membrana filtrante (Al2O3 e argila) foi a mesma para ambos os suportes, sendo composta por uma massa granular cerâmica de baixa porosidade. Os experimentos de filtração foram realizados em temperaturas de 25 a 700 ºC onde mediu-se a capacidade dos filtros de limpar um aerossol de partículas finas polidispersas (diâmetro mediano de 4,6 µm) e calculou-se a eficiência de coleta para diâmetros de partícula entre 0,4 e 8,5 µm. Os resultados mostraram que a eficiência diminuiu com o aumento da temperatura e aumentou com o diâmetro da partícula.

In this work, ceramic filters were used for aerosol filtration. The filters were constituted by two layers, where the first layer was formed by of a highly porous ceramic support with controlled pore size and the second layer constituted by a fine membrane. The ceramic support was obtained from polymeric foams utilizing a technique of alumina impregnation. The supports had 45 and 75 pores per inch (ppi). The membrane (a mixture of alumina and clay) was the same for the two supports, with much smaller pore sizes. The filtration experiments were accomplished at temperatures varying from 25 to 700 ºC, where the ability of the filters for cleaning an aerosol constituted by fine particles (median diameter of 4.6 µm) was measured. The collection efficiency was calculated for particle diameters between 0.4 and 8.5 µm. The results showed that the collection efficiency decreased with the increase of the temperature and increased with particle diameter.

Performance of a wire-plate electrostatic precipitator in the removal of particles with a wide particle size distribution was evaluated. The experimental rig utilized consisted of a set of three precipitators whose dimensions could be varied. It was observed that precipitator performance increased with an increase in the gap between the collecting plates, which resulted in a substantial increase in energy consumption per volume of cleaned gas. The grade efficiency predicted by correlations from the literature did not match the experimental measurements, and a new correlation is proposed.

Ceramic foams are a new structural material, characterized by a high porosity and a large surface area and made of megapores interconnected by filaments. This results in a structure with low resistance to fluid flow, making them appropriate for use as a filter. This work studies the influence of several structural parameters, such as porosity, tortuosity, surface area and pore diameter, in predicting the permeability of ceramic foams. Foams with different pore densities were used as porous media. Permeability was measured utilizing water as the flowing fluid. The results show that the predicted permeability scatters widely with the parameters under study. Pore diameter was the structural parameter that best represented the media. An Ergun-type correlation was fitted to the data and represented very well the permeability of the media in all foams under the experimental conditions studied.