The Effect of Kaolin Concentration on Flock Growth Kinetics in an Agitated Tank

This paper reports on an investigation of the effect of initial solid particle concentrationon flock growth and flock shape characterized by the fractal dimension Df2. The experiments werecarried out in a baffled tank agitated by a Rushton turbine at mixing intensity 64W/m3 and constantdimensionless flocculant dosage DF/ck0 = 4.545 mg/g. The model wastewater (a suspension of tapwater and kaolin) was flocculated with Sokoflok 56A organic flocculant (solution 0.1% wt.). The size and shape of the flocks were investigated by image analysis. The flock growth kinetics was fitted according to a semi-empirical generalized correlation proposed by the authors. The dependences Af = 100.35ck01.532,  df,eq,max = 1.0474ck0-0.311 and (NtF)max = 1622ck0-0.393 were found. The fractal dimension Df2 was found to be independent of flocculation time and initial kaolin concentration, and its value Df2 = 1.470 ± 0.023 was determined as an average for the given conditions

Multi-impurity adsorption model for modeling crystal purity and shape evolution during crystallization processes in impure media

© 2015 American Chemical Society. The impurity effect on the crystal properties, such as particle size and shape distribution, is significant, having significant impact on the downstream processes as well as on the product effectiveness. Currently very few studies exist that provide a quantitative model to describe crystal purity resulting from crystallization processes in impure media, and none to take into account the simultaneous effect of multiple impurities. Hence, the understanding of the effect of multiple impurities on crystallization process is important in order to obtain the desired product properties. Batch crystallization of potassium dihydrogen phosphate from aqueous solution in the presence of impurities was investigated experimentally by using an online particle vision and measurement tool with real-time image analysis. A mathematical model to describe the crystal purity and aspect ratio is proposed based on a morphological population balance equation including primary nucleation, growth of characteristic faces and multisite, competitive adsorption of impurities. The model parameters were identified and validated using crystallization experiments in mixtures of two impurities with variable composition. The developed and validated model can be an efficient tool for the investigation of crystallization processes in impure media with multiple impurities. The model can also serve as an effective tool for process and product design or optimization

Triboelektrische Trennung - Eine neue Methode zur Trennung feiner organischer Pulver?

Triboelectric separation is a technique to separate dry powders according to their ability to generate charge. Charge generation occurs due to the contact of and subsequent separation of two surfaces. A physical description of the triboelectric effect is still unknown. For particles flowing through a tube, particle-particle and particle-wall interaction occur. To enhance separation properties of binary powder mixtures charge generation are enlarged by increasing particle-particle interactions, whereas materials of the tube wall do not influence the separation properties.Die triboelektrische Trennung ist eine Methode, um trockene Pulver durch ihre Ladungserzeugung zu trennen. Die Ladungserzeugung erfolgt durch Kontakt und anschließende Trennung zweier Oberflächen. Eine physikalische Beschreibung des triboelektrischen Effekts ist noch nicht bekannt. Bei Partikeln, die durch ein Rohr strömen, treten Partikel-Partikel und Partikel-Wand Kontakte auf. Ein Erhöhen der Partikel-Partikel Kontakte führt zu erhöten Trenneigenschaften, wohingegen die Materien der Rohrwand diese nicht beeinflussen

A light-scattering study of the kinetic size distribution changes of aerosols

Imperial Users onl

Modelling and control of crystal purity, size and shape distributions in crystallization processes

Crystallization is a key unit operation used for obtaining purified products by many process industries. The key properties of the crystalline products, such as size and shape distribution, purity and polymorphic form are controlled by the crystallization process. All these properties impact significantly the downstream operations such as drying or filtration. Therefore, monitoring and controlling this process is fundamental to ensure the quality of the final product. Process analytical technology (PAT) brings numerous new methods and opportunities in the process analytics and real time process monitoring systems, which can be integrated into the control algorithm and provide high level optimal control strategies as well as deeper understanding of the process. Process monitoring helps develop mathematical models which can, in one hand, help in better understanding the processes and consecvently the development and application of advanced control methods in order to achieve better product quality. In this work, image processing and image analysis based direct nucleation control (IA-DNC) is developed in order to investigate the evolution of the crystal properties, such as crystal size, and crystal shape distribution. The IA-DNC approach is also compared to alternative DNC techniques, in which particle number were measured by Focused Beam Reflectance Measurement (FBRM) in order to control crystal size. A control approach is introduced that control the nucleation and disappearance of crystals during cooling and heating segments related to the changes of the number of counts (measured by Particle Vision Measurment, so called PVM or combination of FBRM and PVM). The approach was applied to investigate crystallization of compounds with different behavior: potassium dihydrogen phosphate (KDP) water, contaminated KDP -water and Ascorbic acid water systems. The results demonstrate the application of imaging technique for model-free feedback control for tailoring crystal product properties. The second main aim of the thesis is to investigate and control crystallization processes in impure media in the presence of multiple impurities, with an impact on the crystal shape via growth kinetics. The broad impact of the crystal growth modifiers (impurities) on the growth kinetics is observed in real time by using in situ video imaging probe and real-time image analysis. A morphological population balance model is developed, which incorporates a multi-site, competitive adsorption mechanism of the impurities on the crystal faces. The kinetic parameters of primary nucleation, growth and impurity adsorption for a model system of potassium dihydrogen phosphate crystallization in water in the presence of two impurities, were estimated and validated with experimental results. It was demonstrated that the model can be used to describe the dynamic evolution of crystal properties, such as size and aspect ratio during crystallization for different impurity profiles in the system. Manual, feedback and hybrid feedback-feedforward control techniques are developed and investigated numerically for continuous processes, while model-based and model-free control approach for crystal shape are developed for batch processes. The developed morphological population balance model is implemented and applied in the model-based control approaches, which are suitable to describe multicomponent adsorption processes and their influence on the crystal shape. Case studies show the effectiveness of crystal growth modifiers based shape control techniques. Comparison of different control approaches shows the effectiveness of the techniques. The third part of the thesis deals with purification of crystals when adsorption of impurities on crystal surfaces and its incorporation into crystals are considered. A purification method, called competitive purity control (CPC) is proposed and investigated. A morphological population balance model, including nucleation, growth and competitive impurity adsorption kinetics is developed to describe the case when multiple impurities can adsorb competitively on the crystal surface. The model is also combined with liquid phase chemical reaction model, in order to investigate the purity control case when an additive is introduced in the system that reacts with the impurity forming a non-adsorbing reaction product. Both competitive purity control approaches proposed: the adsorption based competitive purity control (A-CPC) and the reaction based competitive purity control (R-CPC); are investigated using detailed numerical simulations then compared with the alternative widely used purification method, called recrystallization. In the last contribution chapter, an integrated process optimization of a continuous chemical reactor and crystallizer is performed and studied numerically. The purpose of this study is to show the way in which the byproduct produced in the chemical reactor may affect the crystallization process and how its negative effect can be reduced by applying integrated process optimization. Sensitivity analysis of the system was performed by considering the flow rate and the concentration of substances in the input stream of the chemical reactor as manipulated process variables. Model based integrated process optimization and the sensitivity analysis in order to obtain improved quality product in terms of crystal size, shape and purity

Sediment concentration and particle size in the water column using acoustic methods : Application to the Douro and Minho Estuaries

Most Portuguese fluvial systems are subject to flow regularization through construction of dams and reservoirs. Such structures are responsible for significant changes in estuarine configuration, modifying the natural discharge patterns and trapping the fluvial sediments upstream, decreasing the fluvial contribution to the coastal sediment budget. Sediment export estimates reveal a severe sediment deficit and an accentuated erosive tendency in some segments of the NW Portuguese coast. In this context, the quantification and qualification of the present effective sediment exchanges between estuaries and the coastal shelf is crucial to determine the consequent implications of urgent coastal management actions. In order to address this problem, the implementation of pragmatic monitoring solutions and the compilation of previously collected data has become a priority in order to establish the present sediment dynamic regime in this area. In the past, several long term datasets of Acoustic Doppler Current Profilers were collected in Portuguese transitional areas covering different seasonal regimes. These datasets, collected with diverse objectives in mind, were processed and interpreted to establish the hydrodynamic regime in their respective study areas, but no attempt was made to establish suspended sediment patterns during the duration of their deployment. The possibility of extracting estimates of sediment concentration and grain size from these ADCP datasets is explored in this research, and the results from these findings are then used to reprocess and reinterpret datasets collected in two major NW Portuguese estuaries: The Douro and the Minho. As a final objective we aim to quantify and qualify the effective sediment exchanges from these estuaries and the coastal shelf, and consequently determining the fate and destination of these sediments, by describing different seasonal transport patterns based on sediment dynamics conceptual models of both estuaries built based on previously collected ADCP data time series

Characterization of nanoparticles generated in reacting flows

In this thesis, particle formation in reacting flows is investigated experimentally. Two separate systems are considered. First, silica particle synthesis is characterized in a cold, turbulent jet doped with trace amounts of silane gas that issues into a vitiated co-flow. Additionally, soot formation is characterized in a laminar ethylene diffusion flame. Laser diagnostic techniques are the cornerstone of this work and make it possible to perform measurements with minimal disruption to the system. In both scenarios, elastic light scattering (ELS) and OH-PLIF are employed to obtain experimental signals that contain information about temperature, particle formation, OH concentration and other physical quantities. Additionally, line-of-sight extinction is used in the soot-forming system to recover integrated soot volume fraction profiles and multi-angle light scattering (MALS) is demonstrated on the silica-forming system to obtain in-situ information about particle size. Laser-based datasets are supplemented by probe measurements, including temperature profiles measured using radiation-corrected thermocouples and TEM analysis of particle samples obtained by location-specific thermophoretic sampling. Fully-defined numerical models, available in both scenarios, are validated following an unconventional approach based on the comparison of “predicted signals” with experimentally-obtained signals, as a means to avoid introducing additional assumptions. Satisfactory agreement is found, even though some discrepancies remain concerning silica particle formation, which are likely related to uncertainties in precursor chemistry and nucleation. Nevertheless, this is one of a few joint numerical and experimental studies that address particle formation under turbulent conditions. Regarding soot formation in laminar flames, a consistent underprediction of soot formation on the centreline is identified, which is believed to be a limitation of the acetylene-based model. In summary, this work uses optical diagnostic techniques to generate extensive datasets of particle-forming reacting jets, making a major contribution towards the validation of computational tools to predict particle formation in turbulent reacting flows as well as soot formation in laminar flames.Open Acces

NASA SBIR abstracts of 1992, phase 1 projects

The objectives of 346 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1992 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 346, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1992 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Precipitation and transformation of nanostructured copper oxalate and copper/cobalt composite precursor synthesis

The aim of this thesis was to synthesise and control a nanostructured composite of copper/cobalt. Both the copper and cobalt oxalate exhibit a nanostructure. Attempts to produce nanocomposite particles in the size range of 10-70 nm were made via an oxalate co-precipitation route followed by the appropriate thermal treatment to finally obtain the metal nanocomposite. Much attention was focussed on the understanding of the copper oxalate precipitation and its further transformation into metal before the investigation of the co-precipitation system. One major challenge of this thesis work was to achieve a better understanding of the copper oxalate precipitation mechanism. This was made by following kinetic parameters in order to shed light on the various steps of the precipitation from a supersaturated solution (nucleation, growth and aggregation of nanocrystals). Following the pH as a function of time and using the thermodynamic solubility data it was possible to propose a kinetic model of copper oxalate precipitation, with the co-precipitation of slight amounts (around 0.40% wt) of malachite (CuCO3·Cu(OH)2). The copper oxalate nanostructured particle growth mechanism, from the self-assembly of nanosized buildings blocks, was confirmed for intermediate precipitation times (1-15 minutes). Evidence for such organisation of the particles was shown by a combination of XRD diffraction, SEM and AFM measurements showing the presence of steps at the particle surface with a height that corresponds to a multiple of the mean crystallite size in that particular crystallographic orientation. Further investigations were performed for the early steps of the precipitation by SAXS but either the precipitated volume fraction was too low for detection of the particles or nucleation and growth kinetics were to fast (less than one second) to be followed. The TEM cross-section analyses showed a possible core-shell assembly mechanism. The core showed a random organisation of the crystallites with a size of around 25 nm, while the crystallite in the shell with a size of around 40 nm presented certain order along the 110 axis, particularly towards the particle surface. All these details provided the opportunity to propose a new and more detailed mechanism of the copper oxalate polycrystalline particle formation. In order to master the conditions of the Cu/Cu oxalate decomposition, a good understanding of the simple copper oxalate decomposition was necessary. All along this thesis, much attention was paid to the transformation of the copper oxalate cubic particles into the metal. The objective was thus to conserve the particles cubic macrostructure morphology and their internal nanoscale spatial organisation. To this goaltwo routes were investigated: a direct transformation and another, an indirect one, that required the formation of an oxide. Both the copper oxalate and the oxide showed an anisotropic behaviour during the transformation into the metal. It is shown experimentally that the anisotropy, nanostructure and inhomogeneity of the initial nanocrystallites of both the oxalate and the oxide have an important influence on the mechanism and evolution of transformation into the metal. The particle morphology was shown to be lost for a transformation yield of α>0.80 in the case of the direct transformation from the oxalate whereas the morphology was kept up to the metallic state when passing via the oxide. A kinetic model was proposed for both systems using the method of the sudden change in temperature and pressure. The kinetics analysis did not permit a total understanding of the transformations studied, as several stages were shown to have complex and concurrently competing mechanisms. However, a geometrical model was proposed using the ex-situ analysis of the samples as a function of the reaction yield for both routes. For the initial stages of the copper oxide reduction under He/H2 atmospheres, the kinetic analysis showed hydrogen dissociation as a rate-limiting step. With a view to producing a cobalt/copper composite, preliminary experiments were carried out for the co-precipitation of the Co/Cu oxalate with different cationic ratios. Thermodynamic calculations showed the formation of the two solids was possible independent of the ratio Co/Cu. Experimentally, however a co-precipitation was obtained only for a ratio Co/Cu of 1, whereas for other ration only one single phase (either copper oxalate or cobalt oxalate) was formed. A second route was investigated using cobalt oxalate or cobalt oxide seeds. The amount of the cobalt detected by TEM in the precipitate using either the oxalate or from the oxide seeds was around 3%wt, which is lower than the value of 10%wt necessary to provide desired magnetic properties in the resulting precipitate. The exact nature and spatial distribution of the cobalt was not ascertained and further analysis of the nanostructure by TEM needs to be carried out to confirm the premise of the seed route. This thesis has shown that it is possible to get to a deeper understanding of the kinetics and the mechanism of the copper oxalate precipitation using the appropriate techniques. The cubic macrostructure can be conserved from the initial CuO nanoparticles (13 nm) to metallic Cu (42 nm) by a controlled transformation in a reducing atmosphere. Preliminary experiments made on the possible formation of a Co/Cu composite via the use of the cobalt oxide seeds as heterogeneous nuclei for the copper oxalate precipitation seems most promising