Commande prédictive basée sur la simulation. Application à la flottation en colonne

Les structures de commande prédictive (MPC) utilisant des simulateurs dynamiques comme modèles de procédé ne font pas légion. Cette rareté s'explique en grande partie par la difficulté de résolution des problèmes d'optimisation résultants. En effet, les algorithmes de programmation non linéaire ne sont pas toujours adaptés pour atteindre efficacement l'optimum des fonctions basées sur des modèles physiques, à plus forte raison encore si les équations utilisées sont inconnues (modèles de type boîte noire). C'est en s'appuyant sur ce constat qu'une nouvelle approche pour la MPC est proposée. Le principe consiste à substituer la minimisation explicite de la fonction objectif par une simulation du système en boucle fermée pour solutionner de façon généralement sous-optimale le problème de contrôle en boucle ouverte. Cette nouvelle méthode permet d'exploiter plusieurs des avantages de la commande prédictive sans être limitée par la complexité des modèles. Deux algorithmes sont présentés: décentralisé et découplé. Bien qu'avantageuse sur le plan du réglage, la structure découplée ne permet pas la même liberté que la structure décentralisée pour le choix de l'horizon de prédiction qui doit généralement être du même ordre de grandeur que le temps de réponse en boucle ouverte. Le développement d'une structure de simulation du comportement dynamique de la flottation en colonne, un procédé de séparation des minéraux, représente la seconde contribution de cette thèse. Une grande lacune des simulateurs proposés à ce jour demeure que même lorsque les équations différentielles de conservation sont utilisées, les variations dynamiques du niveau de pulpe ne sont jamais considérées. La structure présentée ici s'intéresse à la simulation des mouvements des phases présentes et de leurs effets sur le niveau de pulpe et sur les débits de sortie. Par ailleurs, comme bien d'autres procédés minéralurgiques, la flottation en colonne a peu bénéficié des avancées en contrôle de procédés. C'est donc sur ce terrain que les deux thèmes étudiés se rencontrent lors d'une mise à l'épreuve conjointe. L'étude de cas proposée s'intéresse à l'asservissement de trois variables d'opération critiques pour le bon fonctionnement du procédé à savoir, la concentration d'air dans la zone de pulpe, le flux net d'eau à l'interface et le niveau de pulpe à l'aide d'un contrôleur prédictif basé sur la simulation.Applications of dynamic simulators for model predictive controllers design are rather scarce in the litterature. The complexity of solving the resulting optimization problems may explain this lack of popularity. In fact, nonlinear programming algorithms are not always well suited to efficiently reach the optimum of a fundamentaly-based cost function. The situation is even worse when the equations used in the model are unknown by the control designers (black box models). The simulation-based model predictive controller is an alternative formulation to perform model predictive control (MPC) without making use of any explicit optimization solver, but rather based on an easy-to-compute closed-loop simulation. The resulting scheme generally provides a sub-optimal solution and benefits from many interesting features of conventional MPC without being restricted by the model complexity. Two algorithms are proposed: decentralized and decoupled. The decentralized simulation structure allows a flexible setting of the prediction horizon (Hp) that is not possible in the decoupled case, easier to tune, but where Hp must generally be in the same order of magnitude that the system settling time. A second contribution of this thesis is the development of a framework for the dynamic simulation of a mineral separation process: column flotation. Until now, most of the proposed models or simulators were restricted to the steady-state behavior. When dynamic mass-balance equations were considered, a constant pulp level during the simulation was always assumed. The presented framework aims to simulate water, solids and gas motion and their effect on the pulp level and output flow rates. As it often happens in mineral processing, the column flotation process has not benefited from advanced control techniques. This is where the two previous subjects merge. The proposed simulation framework is used to design a simulation-based model predictive controller for process variables having a strong influence on metallurgical results (grade and recovery). A case study is presented where the pulp level, bias and air hold-up in the pulp zone are kept within an acceptable operating region

Recent Developments in Flotation Column Instrumentation and Control: An Update

Abstract -For over two decades, LOOP (French acronym for Process Observation and Optimization Laboratory) researchers have been working at developing and/or improving specific sensors for flotation columns and their use for automatic control of this process. Several papers have already been published for the mineral processing industrial and scientific community in peer-reviewed journals and conference proceedings, but very few have been presented in European conferences. This paper summarizes the latest milestones completed by the group. On the instrumentation side, developments encompass a more accurate method for measuring electrical conductivity for flotation column sensors, a device for estimating the bias rate, and a better procedure for evaluating bubble size from images taken by bubble viewers. In terms of process control advances, the discussion will focus on results for bubble size control in a two-phase system, and the application of a 2x2 multivariable predictive control to a pilot flotation column running in parallel to industrial columns in a Québec concentrator. Finally, the latest work on twophase bubble size distribution modeling and control will be summarized

Perspectives of Lithium Mining in Quebec, Potential and Advantages of Integration into a Local Battery Production Chain for Electric Vehicles

This paper presents a discussion on Quebec’s pegmatite lithium resources and potential markets. It also evaluates the opportunities of lithium battery production for electric vehicles (EV) in the province while reducing greenhouse gas emissions. The paper shows that mining Quebec’s lithium ore deposits would be sufficient to satisfy the province’s lithium demand and also for exporting abroad lithium-ion batteries. By considering only the projects whose final product is LMH or LCE, Quebec would be able to produce between 10 and 21 million lithium-ion batteries for electric vehicles with a greenhouse gas emissions footprint of only 43% of the international average value due to Quebec’s hydro power. Finally, considering Quebec’s lithium mining project economics, the increased future demand for lithium would render Quebec’s lithium pegmatite projects competitive compared with those reported for brine projects

Perspectives of Lithium Mining in Quebec, Potential and Advantages of Integration into a Local Battery Production Chain for Electric Vehicles

This paper presents a discussion on Quebec’s pegmatite lithium resources and potential markets. It also evaluates the opportunities of lithium battery production for electric vehicles (EV) in the province while reducing greenhouse gas emissions. The paper shows that mining Quebec’s lithium ore deposits would be sufficient to satisfy the province’s lithium demand and also for exporting abroad lithium-ion batteries. By considering only the projects whose final product is LMH or LCE, Quebec would be able to produce between 10 and 21 million lithium-ion batteries for electric vehicles with a greenhouse gas emissions footprint of only 43% of the international average value due to Quebec’s hydro power. Finally, considering Quebec’s lithium mining project economics, the increased future demand for lithium would render Quebec’s lithium pegmatite projects competitive compared with those reported for brine projects

Enhancing data visualisation to capture the simulator sickness phenomenon: On the usefulness of radar charts

The data presented in this article are related to the research article entitled “The use of transdermal scopolamine to solve methodological issues raised by gender differences in susceptibility to simulator sickness” (Chaumillon et al., 2017) [1]. In an outstanding first demonstration, Kennedy et al. [2] showed that the Simulator Sickness Questionnaire (SSQ) is an appropriate tool to suit the purposes of characterizing motion sickness experienced in virtual environments. This questionnaire has since been used in many scientific studies. Recently, Balk et al. [3] suggested that the proposed segregation of SSQ scores into three subclasses of symptoms might limit the accuracy of simulator sickness assessment. These authors performed a factor analysis based on SSQ scores obtained from nine studies on driving simulators. Although their factor analysis resulted in the same three orthogonal classes of symptoms as Kennedy et al. [2], unlike this pioneering study, no items were attributed to more than one factor and five items were not attributed to any class of symptoms. As a result, they claimed that an exploration of each item score should give additional cues on individual profiles. To gain a better characterization of such item-by-item exploration, data utilised in this research are shown using a radar chart visualisation. Keywords: Simulator sickness, Radar charts, Drivin

Development of a Profitability Analysis Prototype with Multidimensional Benchmarks for Dairy Herds

The prototype of an information visualisation tool was developed using combined information from the Que´bec and Atlantic Provinces Dairy Production Centre of Expertise (Valacta Inc.) and the Quebec Animal Health Records (DSAHR Inc.), with the objective of presenting cumulative lifetime-profit results, and the factors that affect them, thereby facilitating the process of analysing and comparing results at the dairy-herd and individual-cow levels. The information visualisation prototype created benchmarking curves with the possibility to evaluate current profitability at the herd and individual-cow level, and also to monitor the effect of historical decisions and events on the future components of profit. The user is presented with a herd analysis that compares its profit evolution to those of selected cohorts. These values are calculated from the accumulation of average daily profit estimates by herd or cohort. At the individual-cow level, lifetime profit curves are presents that include the effects of health and breeding-service costs among others. It is hoped that this prototype may demonstrate the value, to Dairy Herd Improvement agencies, of analysing and visualizing existing and potential profitability at the herd level, and lifetime analysis at the individual cow level