A methodology for the thermodynamic-kinetic evaluation of circulating systems as TSA carbon capture processes is developed and used in the assessment of a novel CFB configuration against a benchmark (co-current riser). The novel CFB features a counter-current adsorber, a counter-current regenerator and a riser, the latter element playing a double role of solids conveyer and co-current adsorber. The advantages sought by using a counter-current adsorber are not only the more efficient gas-solid contact mode with respect co-current, but also a low pressure drop derived from operation at lower gas velocities and hydrostatic head partially supported on the contactor internals. Knowledge of the adsorption equilibrium alone is sufficient to realise the much higher sorbent circulation rates required by co-current configurations –compared to counter-current– to meet the stringent carbon capture specifications of 90% recovery and 95% purity. Higher solids circulation rates imply higher energy requirements for regeneration, and therefore research and development of co-current gas-solid contactors cannot be justified in terms of searching for energy-efficient post-combustion carbon capture processes. Parallel experimental investigation in the operation and fluid dynamics of cold model CFB rigs is carried out with the purposes of: 1) providing information that may impact the process performance and can be fed into the mathematical model used in the theoretical assessment for more realistic evaluation, and 2) determine gas and solids residence time distributions (RTDs), which are used for the estimation of axial dispersion and comparison with published results in similar systems. Gas RTD data is generated using a tracer pulse injection-detection technique, whereas RTD for the solid phase is studied using positron emission particle tracking (PEPT). The PEPT technique proved to be adequate for the identification of flow regimes in the novel design of the counter-current adsorber, featuring inclined orifice trays. At low gas velocities the particles flow straight down through the tray holes, whereas at higher velocities the particles flow down in zig-zag, increasing the residence time of the particles and reducing the particle axial dispersion, both beneficial in terms of separation efficiency.

Dynamic flow of material has been studied using fast neutron radiography (FNR) and positron emission particle tracking (PEPT). A new fast neutron imaging system was commissioned at The South African Nuclear Energy Corporation, Pretoria, as part of this study, although FNR measurements were ultimately performed at PhysikalischTechnische Bundesanstalt (PTB), Braunschweig. The PEPT studies were undertaken at the PEPT Cape Town facility located at iThemba LABS, Cape Town. The steady state motion of media, within a laboratory-scale tumbling mill, was studied for a range of speed and media mixes, using both FNR and PEPT. Several operational parameters were derived from the data, which could be related to potential improvements to the milling efficiency. The blending of FNR and PEPT data for the study of steady state flow, was explored for the first time. In addition, the flow of water through porous media was studied using FNR, which enabled the determination of the hydraulic conductivity, and hence intrinsic permeability, of the media within the column. The potential of using FNR, without or without PEPT, for the study of material in motion is discussed.

Die Analyse von Kollisionen zwischen Partikeln und Blasen in einer turbulenten Strömung ist ein grundlegendes Problem von hoher technologischer Relevanz, z. B. für die Abtrennung wertvoller Mineralpartikel durch Schaumflotation. Dieser Relevanz steht ein Defizit an experimentellen Daten und Erkenntnissen über den Kollisionsprozess gegenüber. Ein Hauptproblem ist die geringe Anzahl der verfügbaren Messtechniken zur direkten Beobachtung der Kollisionen zwischen Partikeln und Blasen. Daher besteht das Ziel dieser Dissertation darin, neue Methoden zu entwickeln, um die Wechselwirkung zwischen Blasen und Partikeln unter definierten hydrodynamischen Bedingungen zu messen. Diese Methoden beruhen auf der Verfolgung von einzelnen Partikeln mit 4D Particle Tracking Velocimetry (PTV) und Positron Emission Particle Tracking (PEPT), um die Lagrangeschen Partikeltrajektorien in der Nähe einer Blase zu bestimmen und die kollidierenden Partikel zu klassifizieren. In zwei Versuchsaufbauten werden diese Messmethoden angewandt, um die Wechselwirkung zwischen Blasen und Partikeln in turbulenten Strömungen zu untersuchen. In einer Blasensäule wird die Turbulenz im Nachlauf einer frei aufsteigenden Blasenkette erzeugt, während in einem Wasserkanal die Turbulenz durch die Umströmung eines Gitters produziert wird. In beiden Fällen wird das vorhandene turbulente Strömungsfeld um die Blasen mittels Tomographic Particle Image Velocimetry (TPIV) charakterisiert. Zunächst wird der Einfluss des Blasennachlaufs auf die Blasen-Partikel-Kollision für beide Versuchsaufbauten mit dem 4D-PTV-Verfahren analysiert. Es wird gezeigt, dass in beiden Versuchsanordnungen die Kollision von feinen Partikeln nicht nur an der Vorderseite, sondern auch an der Hinterseite der Blase stattfindet. Diese Ergebnisse werden mit der gemessenen turbulenten kinetischen Energie und der Dissipationsrate um die Blase korreliert. Anschließend werden die experimentell ermittelte turbulente kinetische Energie und Dissipationsrate genutzt, um die Kollisionsfrequenz vorherzusagen. Dafür werden bestehende Modelle angewendet und deren Vorhersagen den experimentellen Ergebnissen gegenübergestellt. Weiterhin wird der Wasserkanal genutzt, um den Einfluss der turbulenten Flüssigkeitsströmung auf die Kollision zwischen einer stagnierenden Blase und den Modellpartikeln zu verdeutlichen. Neben der Untersuchung in einer verdünnten Feststoffsuspension wird auch die Blasen-Partikel-Wechselwirkung in einer dichten Strömung mit dem PEPT-Verfahren untersucht. Das PEPT-Verfahren hat das Potenzial, Suspensionen mit einem hohen Feststoffanteil zu messen, was mit optischen Trackingverfahren, wie 4D-PTV, nicht möglich ist. Für den Nachweis einzelner Partikel mit dem PEPT-Verfahren wurden radioaktive Tracerpartikel entwickelt, welche repräsentativ für die Modellpartikeln sind. Die Trajektorien der markierten Partikel werden verwendet, um die durchschnittliche Partikelverteilung im turbulenten Feld zu bestimmen und die Blasen-Partikel-Wechselwirkung zu beschreiben. Insgesamt bieten die entwickelten Methoden eine Möglichkeit die Kollision zwischen Partikeln und Blasen in einer turbulenten Strömung direkt zu untersuchen. Die gewonnenen experimentellen Daten ermöglichen es, bestehende Kollisionsmodelle zu überprüfen und das Verständnis über die Rolle von Turbulenzen in der Schaumflotation zu verbessern. / The analysis of collisions between particles and bubbles in a turbulent flow is a fundamental problem of high technological relevance, e.g. for the separation of valuable mineral particles by froth flotation. That relevance contrasts with an apparent lack of experimental data and insights into this collision process. A major issue is the limitation of available measurement techniques to directly observe the collisions between particles and bubbles. In this dissertation, novel methodologies are developed to measure the interaction between bubbles and particles under defined hydrodynamic conditions. These methodologies comprise particle tracking techniques such as 4D PTV and PEPT to triangulate the Lagrangian particle trajectories in the vicinity of a bubble and classify those which are colliding. In two experimental setups, these techniques are applied to investigate the bubble-particle interaction in turbulent flows. In a bubble column, turbulence is generated in the wake of a freely rising bubble chain, whereas in a water channel, a fluid passing through grid produces a turbulent flow upstream of a stagnant bubble. Accordingly, the turbulent flow field around these bubbles is characterized by TPIV. Firstly, the influence of the bubble wake on the bubble-particle collision is analyzed for both experimental setups with 4D PTV. It is shown that the collision of fluorescent fine particles take place not only at the leading edge but also at the trailing edge of the bubble, independently of the experimental setup. These findings are correlated with the measured TKE and dissipation rates around the bubble and in the bubble wake. Subsequently, the experimental TKE and dissipation rates are applied to existing models for collision frequency, and their predictions are discussed. Secondly, the impact of the turbulent liquid flow on the collision between a stagnant bubble and model particles is studied for a range of turbulent length scales. Besides the investigation in a dilute solid suspension, the bubble-particle interaction is also examined in a dense flow with PEPT. PEPT has the potential to measure suspensions with a high solid fraction, which could not be achieved with optical particle tracking methods. For the detection of individual particles with PEPT, radioactive tracer particles were designed to represent the bulk particles. The trajectories of the labeled particles are used to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. Overall, the developed methodologies in this dissertation provide a framework to investigate directly the collision between particles and bubble in a turbulent flow. The gained experimental validation data allows to verify existing collision models and to advance our understanding of the role of turbulence in froth flotation.