Mônica Lopes Aguiar

A study of the porosity of gas filtration cakes

The purpose of this work was to determine the porosity of gas filtration cakes composed of powdery organic and inorganic materials, employing a technique whereby an optical microscope generates images of the powdery layer deposited on the surface of the filtering medium. To this end, experimental cake filtration porosity data were obtained as a function of the surface filtration velocity. The images generated by the optical microscope were analyzed by using an image analyzing program that supplied the cake porosity values. The results revealed that porosity decreases as surface filtration velocity increases. The average porosity of corn starch was higher than that of tapioca powder and phosphate concentrate, possibly due to the shape of the particles, differences in the physicochemical characteristics of the materials, and grain distribution. Based on the relation of the experimental average porosity data and the filtration velocity, an empirical correlation was found that better fit these parameters.

Influence of removal time and particle size on the particle substrate adhesion force

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.

Recovery of valuable materials from spent NIMH batteries using spouted bed elutriation.

In recent years, a great increase in the generation of spent batteries occurred. Then, efficient recycling ways and correct disposal of hazardous wastes are necessary. An alternative to recover the valuable materials from spent NiMH batteries is the spouted bed elutriation. The aim of this study was to apply the mechanical processing (grinding and sieving) followed by spouted bed elutriation to separate the valuable materials present in spent NiMH batteries. The results of the manual characterization showed that about 62 wt.% of the batteries are composed by positive and negative electrodes. After the mechanical separation processes (grinding, sieving and spouted bed elutriation), three different fractions were obtained: 24.21 wt.% of metals, 28.20 wt.% of polymers and 42.00 wt.% of powder (the positive and negative electrodes). It was demonstrated that the different materials present in the spent NiMH batteries can be efficiently separated using a simple and inexpensive mechanical processing.

The Influence of Particulate Matter and Filtration Conditions on the Cleaning of Fabric Filters

Thick filter cakes have to be removed from the filter in order to keep the pressure drop down to a suitable level for the filtration process of gases. The influence of both, the particulate matter used (phosphate rock, manioc starch and magnesium silicate) and the operating parameters during filtration of these particles from gas on the filter cake removal, was studied. Three filtration velocities were used (0.06, 0.09 and 0.11 m s−1) which were maintained constant until achieve predetermined values of pressure drop (500; 600 and 700 mm of H2O). The cleaning of the filter was performed using the reverse flow technique applying different gas velocities (0.007; 0.015; 0.030; 0.045 and 0.060 m s−1). For all the particulate matters studied, the adhesion force increased with the increment of the filtration gas velocity. The percentage of cake removal for manioc starch and magnesium silicate particles was ∼90% while for phosphate concentrate was ∼60%. Thus, the values of adhesion force per unit area were higher for phosphate concentrate than the other particulate matter.

Performance of a Venturi scrubber in the removal of fine powder from a confined gas stream

Experimental results on the performance of a laboratory scale rectangular Venturi scrubber in the removal of fine mineral particles from a confined air stream are presented, and a new correlation is proposed and evaluated. The scrubber was operated with air velocities in the throat varying from 58 m/s to 75 m/s and liquid flow rates varying from 280 ml/min to 900 ml/min. Liquid was injected as a jet emerging from a 1.0 mm orifice at the throat. Results for dust collection grade efficiency varied from 87% to 98% for particles from 0.1 µm to 2.0 µm.

Fluid Dynamics Study of the Influence of the Position of the Feed in Fabric Filters

Abstract The fabric filter is a pioneering piece of equipment used to reduce the emission of small size particulate matter from industrial sources. It is relatively inexpensive and offers easy operation and high efficiency of collection for a wide range of sizes. Aiming at making the filtration operation more efficient and economical, this work investigated the best position of the feed in the filtration box and, consequently, the best way to clean the fabric filter. The cleaning system used in fabric filters is of great importance for the efficiency and durability of the equipment, and it defines the position of the dirty gas inlet in the filtration box. This work used CFD (Computational Fluid Dynamics) techniques to simulate the pressure drop and the fluid dynamics of the gas as a function of the position of the feed, which was varied from the top to bottom of the filtration box. The simulations were carried out using a new polyester filter for each feed position. According to the results, the fluid should be fed next to the bottom of the filtration box, which produces a smaller pressure drop, a better distribution of the gas and less wear of the bags adjacent to the gas feed.

Atmospheric particulate matter in the city of Sao Carlos/SP, Brazil

This paper presents experimental data and source apportionment simulations on particulate matter (PM10 and PM2.5) in the atmosphere of Sao Carlos/SP, Brazil. Both a Hi-vol sampler equipped with glass fibre filters and a Dichotomous sampler with nucleopore filters were used. The collected material was analysed for total carbon, using a thermometric method, and for traces of several chemical species, using X-ray fluorescence spectroscopy. Source apportionment estimations were made with a chemical mass balance receptor model software (CMB8), with source profiles taken and adapted from the literature. The results indicate that both PM10 concentration and source apportionment vary seasonally, and that vegetative burning can be a significant source of PM10 in the dry season

Performance of fibrous filters during nanoparticle cake formation

ABSTRACT Fibrous filters are highly efficient in removing micrometer particles, but their performance in the nanometer particle range is still little known. The aim of this study was to evaluate pressure drop and collection efficiency during nanoparticles cake formation using commercial fibrous filters. The filter media used were High Efficiency Particulate Air (HEPA) and polyester filters. The aerosols were generated by a commercial inhaler using a 5 g/L solution of NaCl and the particles produced were in the size range from 6 to 800 nm, with a peak at around 40 nm. A superficial velocity (vs) of 0.06 m/s was employed. During the filtration, the maximum pressure drop established was ∆P = ∆Pf +980Pa, where ∆Pf is the initial pressure drop of the filter. The collection efficiency was determined for a clean filter and for intermediate pressure drops. The filtration curves obtained showed that the HEPA filter provided greater surface filtration, compared to the polyester filter. Comparison of the collection efficiencies for clean filters revealed that the HEPA filter was highly efficient, even in the absence of cake, while the polyester filter showed initial collection efficiencies of between 20 and 40% for particles in the size range from 100 nm to 1000 nm. However, after formation of the filter cake, the collection efficiencies of both filters were almost 100% during the final stage of filtration. This shows that the fibrous filter can be applied in several industrial processes with highly efficient nanoparticle separation, after the formation of a thin layer cake filtration.

The Effect of the Dust Cake Resistance on Fluid Flow Passing through the Filter Media

A filter box was used to obtain the experimental data of filtration operation with different air velocities as 5, 10 and 15 cm/s. The experimental data were compared to the simulated ones using CFD technique. For all range of air velocity and dust cake porosity and permeability employed, data of pressure drop in filter box could be satisfactorily predicted by simulations in CFD. Furthermore, the CFD simulations showed that undesirable patchy cleaning might be overcome using air velocities lower than 15cm/s.

Centrifuge Study on Influence of Particle Size, Compression and Substratum on Particle-Surface Adhesion Force

The centrifugal technique was used to investigate the influence of particle size, applied compression and substrate materials (stainless steel, glass, Teflon® and PVC) on particle-surface adhesion force. Phosphate rock and manioc starch particles were used in a microcentrifuge that contained specially designed centrifuge tubes and reached a maximum rotation speed of 14,000 rpm. The profile of adhesion force followed a log-normal distribution and adhesion force increased linearly with particle size and the increment of the compression force. The manioc starch particles presented adhesion forces greater than those for the phosphate rock particles for all particle sizes studied. The glass substrate showed a higher adherence than other materials, most probably due to its hardness and polishing.