Multivariate statistical analysis of Hall-Héroult reduction cells : investigation and monitoring of factors affecting performance

Les cuves d'électrolyse utilisées pour la production aluminium sont soumises à des variations de la qualité des matières premières, à des perturbations diverses encourues en cours de production ou en cours de démarrage. Il est connu que ces perturbations ont un impact sur la durée de vie des cuves ainsi que sur l'efficacité de production, métallurgique et énergétique. L'amélioration des performances passe nécessairement par une meilleure compréhension des sources de variations. Plusieurs travaux ont été présentés jusqu'à présent par le biais d'études univariées entre les différents facteurs et les performances. Cependant, dans ces études, le comportement des cuves n'est pas étudié de manière multivariée, ce qui ne permet pas d'étudier les interactions entre les différentes variables. Cette thèse propose d'étudier les facteurs affectant les performances des cuves d'électrolyse, précisément la duré de vie, le rendement Faraday et la consommation énergétique, par le biais de méthodes statistiques multivariées (PCA et PLS). Premièrement, il est démontré que la durée de vie des cuves est expliquée à 72% en utilisant l'information provenant des préchauffages, des démarrages et de l'opération transitoire, démontrant ainsi l'effet de ces étapes sur la durée de vie des cuves. Cette étude est suivie d'une analyse des facteurs affectant l'efficacité de courant et la consommation énergétique des cuves. L'effet de la qualité de l'alumine, des anodes, des variables manipulées, et des variables d'états des cuves permet d'expliquer 50% des variations des performances. Cette étude démontre l'importance du contrôle de la hauteur de bain. Ainsi, une étude approfondie des facteurs affectant la hauteur de bain est effectuée. La composition du produit de recouvrement des anodes a un impact majeur sur la hauteur de bain. Malheureusement, il est présentement impossible de bien effectuer le suivi et le contrôle de cette composition puisque seulement quelques échantillons sont analysés quotidiennement. Afin de palier à ce manque, cette thèse présente une nouvelle approche, basée sur l'analyse d'image, pour prédire la composition du produit de recouvrement. Cette application faciliterait le suivi et le contrôle de la composition, ce qui améliorerait le contrôle de la hauteur de bain permettant ainsi d'améliorer les performances des cuves

How do you look at what you touch?:a study of touch interaction and gaze correlation on tablets

The comprehension of the correlation between hand and gaze is important in HCI as it provides foundations to build rich and natural user experiences on devices. Despite the interest in describing this correlation in Internet-related activities, notably search activities, the studies that have been done so far only focus on the mouse as the proxy for the hand. Thanks to the touchscreen, tablets allow us to investigate the hand-eye correlation with direct touch input instead. We designed a gaze and touch data collection via a user study involving Internet-based tasks on a tablet in order to explore the data, detail the correlation between touch input and gaze, and in a further step, use these results to suggest a gaze prediction model based on touch and context

Investigation of the Frozen Bath Layer under Cold Anodes

Hall-Héroult cell stability is highly affected by anode changing operations. Upon the insertion of a cold anode in the cell, a layer of molten cryolite freezes under the anode. The thickness, microstructure, and chemical composition of this layer vary as a function of time and its location in the cell. To better understand the evolution of the frozen layer, mandatory for the validation of numerical models, a measurement campaign was conducted on the anodes having a few hours of operation in the cell. The macrostructure of the selected frozen bath samples has been investigated using computed tomography while scanning electron microscope (SEM) has been used to qualify its microstructure. An energy-dispersive X-ray spectroscope (EDS) coupled to the SEM has revealed the chemical content. The results showed not only very different macrostructures between samples, but also significantly heterogeneous structure within the same sample. Nevertheless, for all samples, there is a clear distinction between the frozen cryolite and alumina/dusting phases, with the latter surrounding the cryolite matrix

The Potential of Acousto-Ultrasonic Techniques for Inspection of Baked Carbon Anodes

High quality baked carbon anodes contribute to the optimal performance of aluminum reduction cells. However, the currently decreasing quality and increasing variability of anode raw materials (coke and pitch) make it challenging to manufacture the anodes with consistent overall quality. Intercepting faulty anodes (e.g., presence of cracks and pores) before they are set in reduction cells and deteriorate their performance is therefore important. This is a difficult task, even in modern and well-instrumented anode plants, because lab testing using core samples can only characterize a small proportion of the anode production due to the costly, time-consuming, and destructive nature of the analytical methods. In addition, these results are not necessarily representative of the whole anode block. The objective of this work is to develop a rapid and non-destructive method for quality control of baked anodes using acousto-ultrasonic (AU) techniques. The acoustic responses of anode samples (sliced sections) were analyzed using a combination of temporal features computed from AU signals and principal component analysis (PCA). The AU signals were found sensitive to pores and cracks and were able to discriminate the two types of defects. The results were validated qualitatively by submitting the samples to X-ray Computed Tomography (CT scan)

Inspection of Prebaked Carbon Anodes Using Multi-Spectral Acousto-Ultrasonic Excitation

Reduction cell operation in primary aluminum production is strongly influenced by the properties of baked anodes. Producing consistent anode quality is more challenging nowadays due to the increasing variability of raw materials. Taking timely corrective actions to attenuate the impact of raw material fluctuations on anode quality is also difficult based on the core sampling and characterization scheme currently used by most anode manufacturers, because it is applied on a very small proportion of the anode production (about 1%), and long-time delays are required for lab characterization. The objective of this work is to develop rapid and non-destructive methods for the inspection of baked anodes. Previous work has established that sequential excitation of smaller parts collected from an industrial sized anode using acousto-ultrasonic signals at different frequencies allowed detecting and discriminating anode defects (pores and cracks). This was validated qualitatively using X-ray computed tomography. This work improves the method by using frequency-modulated excitation and building quantitative relationships between the acousto-ultrasonic signals and defects extracted from tomography images using Wavelet Transforms and Partial Least Squares (PLS) regression. The new excitation approach was found to provide similar or better inspection performance compared with sequential excitation, while requiring a shorter cycle time

A two-part Phase II study of cediranib in patients with advanced solid tumours: the effect of food on single-dose pharmacokinetics and an evaluation of safety, efficacy and imaging pharmacodynamics

Background: Cediranib (RECENTIN™) is an oral, highly potent VEGF inhibitor. This study evaluated the effect of food on the pharmacokinetics of cediranib and compared the administration of continual cediranib via two dosing strategies using this as a platform to investigate pharmacodynamic imaging biomarkers. Methods: Sixty patients were randomised to receive two single doses of cediranib in either fed/fasted or fasted/fed state (Part A). In continual dosage phase (Part B), patients were randomised to a fixed-dose or dose-escalation arm. Exploratory pharmacodynamic assessments were performed using DCE-MRI and CT enhancing fraction (EnF). Results: In part A, plasma AUC and C max of cediranib were lower in the presence of food by a mean of 24 and 33%, respectively (94% CI: AUC, 12–34% and C max, 20–43%), indicating food reduces cediranib plasma exposure. In part B, cediranib 30 mg/day appeared to be the most sustainable for chronic dosing. Continuous cediranib therapy was associated with sustained antivascular effects up to 16 weeks, with significant reductions in DCE-MRI parameters and CT EnF. Conclusions: It is recommended that cediranib be administered at least 1 h before or 2 h after food. Evidence of antitumour activity was observed, with significant sustained effects upon imaging vascular parameters.</p