1,721,019 research outputs found
The effect of impeller-stator design on froth stability, flotation performance and flotation hydrodynamics
Full text linkFroth flotation is the most important mineral concentration process. Over the last few decades, throughput has increased due to flotation equipment becoming exponentially larger. Small improvements in performance, therefore, significantly impact the economic revenue and sustainability of the process. The optimisation of flotation has thus been extensively studied, resulting in several improvements, especially in operating conditions, and important advances in our understanding of flotation. Publications on flotation equipment designs and their impact on flotation phenomena, however, are scarce and flotation tank design has, to a large extent, remained in-house know-how of manufacturing companies. Currently, flotation tank design tends to focus mainly on pulp zone parameters without considering its effect on the froth zone, despite the importance of froth stability in flotation performance. Moreover, while most new designs are studied using computational fluid dynamics models, these are typically validated with one- or two-phase systems, which oversimplify flotation phenomena. To solve these problems, large experimental datasets quantifying the effects of design variables on flotation phenomena are required.
This thesis fills these and other gaps identified in the literature, by studying the effects of different impeller-stator designs on flotation phenomena. A continuously overflowing laboratory-scale flotation tank was used to study two different impeller designs, a Rushton turbine and a rotor, both with and without a stator. Bubble size distribution was measured for two- and three-phase systems, froth stability was quantified using air recovery, and flotation performance was assessed. Furthermore, a scaled-down bench-scale flotation cell was used to study the effect of these impeller-stators on the hydrodynamics of the flotation system, using Positron Emission Particle Tracking, which determines the motion of radioactive particle tracers, representative of hydrophobic and hydrophilic particles.
Results show that the effect of the stator is predominant over the effect of impeller design. This thesis quantifies, for the first time in the literature, stator-induced bubble size reduction, caused by changes in bubble size distribution. Similarly, it shows for the first time that stators enhance froth stability and drastically change the hydrodynamics of the system by altering flow patterns and particle speed. All these effects improve flotation performance, markedly increasing metallurgical recovery. The information presented herein allows for a better understanding of physical phenomena within a flotation tank. Moreover, these datasets represent an important contribution to the validation and improvement of three-phase computational fluid dynamics models and will be valuable for the design of pilot- and industrial-scale test work.Open Acces
Tank design modifications for the improved performance of froth flotation equipment
Full text linkFroth flotation is a physico-chemical technique used to separate the constituents of a mixed mineral slurry by their relative surface hydrophobicity. In order to do so economically, it is necessary to treat large volumes of material in ever-larger and more efficient tanks. The efficiency and efficacy of such tanks can be enhanced through mechanical modifications designed to improve froth handling,
increase the likelihood of bubble-particle interactions in the pulp, and increase the residence time of suspended solids in the tank. However, design modifications suggested by computational modelling or bench-scale experiments often do not realise performance improvements at pilot and plant-scale because of imperfect scale-up from bench-scale, and differences in the type and intensity of the sub-processes affecting performance at different scales. The first outcome of this thesis is an intermediate, laboratory-scale froth flotation circuit that more closely resembles continuously-operated pilot-scale equipment, but which is better instrumented and controlled. This work describes not only the laboratory-scale system, but also detailed regression models of its behaviour and performance based on extensive monitoring and instrumentation. The resultant performance models provide a baseline against which to test design modifications, and the resultant behaviour models inform the design of such modifications. The second outcome of this thesis, a performance-enhancing design modification, was prompted by the discovery that minimising the variability of the pulp-froth interface leads to an increase in both indicative grade and recovery. The resultant tank modification was a horizontal mesh inserted into the pulp below the pulp-froth interface, designed to isolate it from the turbulent region around the impeller. The mesh pore size and thickness, and the position at which it was installed in the tank, were taken as design variables to be optimised by the genetic algorithm method. The result is a grade-recovery curve corresponding to an optimal mesh pore size of 123.4 +/- 3.1 mm. From this curve it was found that increasing the mesh thickness from 33 mm to 47 mm yields a maximum improvement in the recovery of 18.9% without compromising the grade, and increasing the depth of the mesh from 200 mm to 250 mm below the pulp-froth interface yields a maximum improvement in the grade of 3.2% without compromising the recovery. This grade-recovery curve, and the insights gained during the process of design and refinement, provides the rationale for a proposed program of mesh tests at pilot-scale.Open Acces
Numerical modelling of polydispersed flows using an adaptive-mesh finite element method with application to froth flotation
Full text linkAn efficient numerical framework for the macroscale simulation of three-phase polydispersed flows is presented in this thesis. The primary focus of this research is on modelling the polydispersity in multiphase flows ensuring the tractability of the solution framework. Fluidity, an open-source adaptive-mesh finite element code, has been used for solving the coupled equations efficiently.
Froth flotation is one of the most widely used mineral processing operations. The multiphase, turbulent and polydispersed nature of flow in the pulp phase in froth flotation makes it all the more challenging to model this process. Considering that two of the three phases in froth flotation are polydispersed, modelling this polydispersity is particularly important for an accurate prediction of the overall process. The direct quadrature method of moments (DQMOM) is implemented in the Fluidity code to solve the population balance equation (PBE) for modelling the polydispersity of the gas bubbles. The PBE is coupled to the Eulerian--Eulerian flow equations for the liquid and gas phases. Polydispersed solids are modelled using separate transport equations for the free and attached mineral particles for each size class.
The PBE has been solved using DQMOM in a finite element framework for the first time in this work. The behaviour of various finite element and control volume discretisation schemes in the solution of the PBE is analysed. Rigorous verification and benchmarking is presented along with model validation on turbulent gravity-driven flow in a bubble column. This research also establishes the importance of modelling the polydispersity of solids in flotation columns, which is undertaken for the first time, for an accurate prediction of the flotation rate. The application of fully-unstructured anisotropic mesh adaptivity to the polydispersed framework is also analysed for the first time. Significant improvement in the solution efficiency is reported through its use.Open Acces
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Modelling the transient drainage of liquid in foams
Full text linkFroth flotation is the largest tonnage separation process worldwide and is used for
paper deinking, water purification and, particularly, mineral separation. One of the key
aspects of the performance of
flotation cells is the behaviour of the liquid within the
froth, as it is crucial to the purity of the product and a major influence on the overall
recovery. Nonlinearities in models for liquid motion in the froth make them complex to
solve and existing numerical solutions have been in two dimensions at most. In order to
predict the performance of industrial
flotation cell designs, a three-dimensional solution
for these equations is desirable. Moreover, the understanding of the process would be
enhanced if a transient model were used to predict the dynamics of foam drainage.
In this work, the equations for the liquid drainage have been rearranged in order to
make them analogous to a compressible version of the Navier-Stokes equations, coupled
to an equation of state. A model for predicting the movement of the flowing foam
has also been developed, which is able to solve for the foam velocity in two and three
dimensions. This has allowed the transient behaviour of liquid in flotation foams to
be modelled using Fluidity, a general purpose finite element method code that allows
simulations to be carried out on unstructured adaptive meshes. This is an important
feature for improving the computational cost of modelling these systems, as there are
boundary layers present in the process, whose size is independent of the scale of the
flotation system being modelled.
These models have allowed, for the first time, to carry out numerical investigations
of drainage for arbitrary
flotation tank geometries in up to three dimensions, and have
been verified against analytical solutions and compared to laboratory scale experiments
with satisfactory agreement
The development of multiple criteria decision making methods with applications to the selection problem in mining and mineral processing
Full text linkOver the past decade, decision makers in the mining and mineral processing industry have had to deal with multiple challenges such as varying metal prices, depleting resource quality, and complying with stricter environmental regulations. Besides, the mining and mineral processing industry also needs to consider the use of renewable energy in order to comply with strict environmental regulations. In addition, since the use of renewable energy has costs associated to the additional equipment installation and maintenance, optimizing the equipment selection to minimise energy costs is of vital importance. Therefore, decision makers in the sector often face problems that involve multidisciplinary knowledge that take into account technical, social, economic and environmental aspects.
Multiple Criteria Decision Making (MCDM), which is a part of operations research, has become extremely useful to overcome a variety of decision making problems in mining and mineral processing. Although a very large number of MCDM methods have been developed, the effectiveness of these methods still depends on the objective of the decision making process (i.e. selection, sorting, ranking, description) and the nature of the problem.
An exhaustive literature review on the applications and trends of MCDM for the selection problem in mining and mineral processing has been conducted in this work. The literature review indicates that conventional MCDM methods have been frequently criticised on several drawbacks including its inability to quantify the uncertainty in data and information, the occurrence of the rank reversal phenomenon, and its difficulty in aggregating several judgements and preferences from multiple decision makers including related uncertainty on their judgements or preferences, as well as the robustness of MCDM methods in dealing with non-homogenous data (i.e. quantitative and qualitative).
This thesis presents the development of four new MCDM methods and their application to the selection problem (i.e. determining the best option from a set) in mining and mineral processing by taking into account the role of uncertainties in the decision making process. This work mainly demonstrates the value of applying the concept of constrained fuzzy arithmetic in fuzzy extension of conventional MCDM methods when the input data that need to be analysed are difficult to define precisely. In order to showcase the capability of the developed methods, three case studies on the selection problem in the mining industry were conducted. Furthermore, the robustness of the developed methods are shown by conducting sensitivity analyses and comparing their results to those obtained from existing methods.Open Acces
Design and optimisation of mini-hydrocyclones for the separation of particles in the micron size range
Full text linkThe use of mini-hydrocyclones (e.g. 10 mm in diameter) for the separation of par-ticles in the micron range is of growing interest in industry. However, these hydro-cyclones are typically limited to conventional shapes or restricted to specific outletsizes, which can lead to sub-optimal performance. Mini-hydrocyclones exhibit abypass fraction that is larger than the water recovery, resulting in a high particlerecovery to the underflow, as well as low water recovery, which is convenient fordewatering processes. However, this larger bypass fraction can be a disadvantagewhen the purpose of the hydrocyclone is particle classification, because of the largeamount of fine particles that are misplaced in the underflow. Therefore, a deeperunderstanding of the mini-hydrocyclones performance is needed.The aim of this thesis is to present a method for the optimisation of mini-hydrocyclonedesign. The method consists of designing and 3D printing mini-hydrocyclones, car-rying out Computational Fluid Dynamics (CFD) simulations, and performing ex-perimental tests. 3D printed mini-hydrocyclones were tested and the effect thatchanges in vortex finder and spigot diameters have on separation performance wasstudied. A CFD model was implemented and validated with experimental data formini-hydrocyclones applied to dewatering and classification processes. Lastly, noveldesign of hydrocyclones (i.e. with parabolic walls) were studied in a full factorialand Central Composite Rotatable (CCRD) designs.The first outcome of this thesis is the application of the 3D printing technologyfor practical and rapid prototyping of mini-hydrocyclones. The second outcome isthe implementation of a validated CFD model to predict the performance of mini-hydrocyclone for dewatering and particle classification processes. The third outcomeis the combination of 3D printing technology and the CFD model to evaluate hydro-cyclones with parabolic walls. This thesis demonstrates the potential of 3D printing,CFD modelling and robust experimental testwork to improve the understanding ofmini-hydrocyclones performance in dewatering and classification processes.Open Acces
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