Fundamental understanding of swirling flow pattern in hydrocyclones

This work is concerned with establishing and validating a physics-based model that describes the swirling flow inside hydrocyclones. The physics is embedded in a Computational Fluid Dynamics (CFD) simulation model whose key features are presented and justified in the paper. Some features are selected in such a way that the model can eventually be used to simulate dense flow inside hydrocyclones. Nevertheless, its underlying physics is here within validated against dilute flow conditions. The model applies a Eulerian multi-fluid modelling approach for fluid–particle turbulent flows, and is computed using the semi-industrial code NEPTUNE_CFD. Simulation results are successfully compared to water split, velocity profiles inside the hydrocyclone and partition function measurements, either produced using our own experimental setup or from the literature. The work finds velocity profiles to be the most discriminating parameter for validation of the physics that describes the swirling flow inside the hydrocyclone. Water split on the other hand shows no relation to the choice of turbulence model and hence cannot be used to validate a mechanistic model of the hydrocyclone. The physics-based model presented here is the first building block towards describing and understanding hydrocyclone flow under dense regime

Analysis of swirling flow in hydrocyclones operating under dense regime

There are many circumstances where hydrocyclone performance and dense flow are intertwined, such as for example when feed solids flow exceeds hydrocyclone capacity during continuous operations. The work reported here, which is part of an ongoing research effort to develop a robust CFD model for prediction of hydrocyclone performance, focuses on hydrocyclone operation under high solids concentration. The paper presents the basic physics framework that accounts for solid–liquid and solid–solid interactions under hydrocyclone’s swirling flow. Operating conditions that are past the transition from spray to rope regime are deliberately chosen for this purpose. Model predictions are validated by comparison with solids split and separation curves measured on a 100 mm diameter hydrocyclone. CFD model predictions permit taking an insightful look at the inside of a hydrocyclone under extreme operating conditions, which would be difficult to achieve experimentally. Velocity profiles, G-force distribution and distribution of solids predicted by CFD are bound to lead to a better understanding of the separation that takes place inside a hydrocyclone, which may eventually help improve hydrocyclone design and performance

Is the fish-hook effect in hydrocyclones a real phenomenon?

Although the fish-hook effect has been reported by many for a very long time, scientists and practitioners alike share contradictory opinions about this phenomenon. While some believe that it is of physical origin, others opine that it is the result of measurement errors. This article investigates the possibility that the fish-hook effect could indeed be measurement error related. Since all the experimental errors are embedded in the raw size distribution measurements, the paper first lays down the steps that lead to estimation of the partition function and confidence bounds, which are seldom reported in hydrocyclone literature, from the errors associated with the experimental size distribution measurements. Using several data sets generated using a 100 mm diameter hydrocyclone operating under controlled dilute to dense regimes, careful analysis of the partition functions following the developed methodology yields unambiguous evidence that the fish-hook effect is a real physical phenomenon. An attempt is also made to reunite some of the major contradictory views behind the existence of the fish-hook based on sound statistical arguments

Effet de la concentration en solide sur les performances de séparation d'un hydrocyclone (simulations numériques et expériences de références)

L'exploitation minière des sables bitumineux requiert une succession de nombreuses opérations pour séparer le bitume, l'eau et le sable. La séparation solide/liquide fait intervenir un hydrocyclone. Afin de limiter l'ajout d'eau, l'hydrocyclone doit fonctionner dans des conditions inhabituelles correspondant à une concentration élevée à l'alimentation. Une étude expérimentale a permis de caractériser l'ensemble des régimes de fonctionnement, l'influence de la concentration et des caractéristiques géométriques. De plus, des simulations numériques ont été réalisées avec NEPTUNE_CFD@Tlse. Deux méthodes sont proposées pour modéliser les comportements observés à faible et à forte concentration. Les résultats numériques sont en bon accord avec les expériences sur toute la gamme de concentration. L'étude des phénomènes locaux permet une meilleure compréhension des mécanismes de séparation. ABSTRACT : Tar sands beneficiation requires a series of processing steps for separation of bitumen, water and sand particles. In this process, hydrocyclones are used to separate sand from water and bitumen, thereby recovering additional bitumen and concentrating sand particles before sending them off to tailing ponds. In order to reduce fresh water consumption (environmental policy), hydrocyclones need to operate with high feed solids content, say 50% in mass, which lays outside their standard operating regime. The response and performance of hydrocyclones need to be understood under such stringent operating conditions. A pilot scale experiment was commissioned for testing a 100mm diam. hydrocyclone under different operating regimes of discharge and measuring the corresponding separation performance. Feed solids concentration and geometrical properties were varied extensively. Separation performance indicators, including partition curve, cut-size, sharpness index and water recovery to underflow were obtained by standard data reconciliation. The experimental data provided all the information required to test the CFD model that was derived to simulate the hydrocyclone. Eulerian simulations of the three-dimensional liquid-solid flow inside the hydrocyclone were carried out, using a multi-fluid model (NEPTUNE_ CFD@Tlse). The actual geometrical features and operating conditions of the hydrocyclone were accurately matched in the simulations. Two simulation approaches have been proposed for hydrocyclone modelling, depending on their operating under dilute conditions, with a spray discharge or dense conditions, with a rope discharge. Numerical simulation results are in good agreement with experiments. Local analysis of hydrodynamic features yields new insights into the behaviour of hydrocyclones at high feed solids concentration

Understanding the effect of solids concentration on hydrocyclone performance (CFD and experiment)

L'exploitation minière des sables bitumineux requiert une succession de nombreuses opérations pour séparer le bitume, l'eau et le sable. La séparation solide/liquide fait intervenir un hydrocyclone. Afin de limiter l'ajout d'eau, l'hydrocyclone doit fonctionner dans des conditions inhabituelles correspondant à une concentration élevée à l'alimentation. Une étude expérimentale a permis de caractériser l'ensemble des régimes de fonctionnement, l'influence de la concentration et des caractéristiques géométriques. De plus, des simulations numériques ont été réalisées avec NEPTUNE_CFD@Tlse. Deux méthodes sont proposées pour modéliser les comportements observés à faible et à forte concentration. Les résultats numériques sont en bon accord avec les expériences sur toute la gamme de concentration. L'étude des phénomènes locaux permet une meilleure compréhension des mécanismes de séparation.Tar sands beneficiation requires a series of processing steps for separation of bitumen, water and sand particles. In this process, hydrocyclones are used to separate sand from water and bitumen, thereby recovering additional bitumen and concentrating sand particles before sending them off to tailing ponds. In order to reduce fresh water consumption (environmental policy), hydrocyclones need to operate with high feed solids content, say 50% in mass, which lays outside their standard operating regime. The response and performance of hydrocyclones need to be understood under such stringent operating conditions. A pilot scale experiment was commissioned for testing a 100mm diam. hydrocyclone under different operating regimes of discharge and measuring the corresponding separation performance. Feed solids concentration and geometrical properties were varied extensively. Separation performance indicators, including partition curve, cut-size, sharpness index and water recovery to underflow were obtained by standard data reconciliation. The experimental data provided all the information required to test the CFD model that was derived to simulate the hydrocyclone. Eulerian simulations of the three-dimensional liquid-solid flow inside the hydrocyclone were carried out, using a multi-fluid model (NEPTUNE_ CFD@Tlse). The actual geometrical features and operating conditions of the hydrocyclone were accurately matched in the simulations. Two simulation approaches have been proposed for hydrocyclone modelling, depending on their operating under dilute conditions, with a spray discharge or dense conditions, with a rope discharge. Numerical simulation results are in good agreement with experiments. Local analysis of hydrodynamic features yields new insights into the behaviour of hydrocyclones at high feed solids concentration

Evaluation of the forces on a control drive mechanism adaptor thermal sleeve using CFD

International audienceWear due to hydraulic forcing has been observed on the control rod drive mechanism adaptor thermal sleeves in some pressurized water reactors. The thermal sleeves protect the control rod drive mechanism adaptor and extend into the closure head assembly or dome region above the upper plenum. Preliminary analyses indicate that flow in the dome is the primary source of the forcing. In this paper, flow conditions representative of those that occur around a thermal sleeve are studied in order to evaluate and quantify the hydraulic forcing on the thermal sleeve. The simulations are carried out using large eddy simulations (LES) on tetrahedral grids. Results using two different codes (Code_Saturne from EDF and TrioCFD from the CEA) are compared. Some benchmark flows such as steady channel flow are also studied to consolidate the comparisons. It is found that the downward force on the thermal sleeve is approximately 1.5N when the inlet velocity is 1 m/s and 6N when the inlet velocity is 2 m/s. The RMS fluctuation of the force is approximately 0.07N and 0.3N respectively

Use of CFD as a design tool for a phospheric acid plant cooling pond

Phosphate fertilizer plants are installations constantly evolving which make their design a challenging task. Phosphogypsum, a by-product of the manufacture of phosphoric acid, is piled up, forming stacks which may eventually alter the process efficiency as they encroach on process cooling ponds and locally modify the airflow fields. The easier access to high performance computing and the improvement of software capabilities allow to fully consider today the use of CFD within tight-schedule industrial projects, even the ones involving large-size geometry. As an example we describe how CFD can be efficiently used as a design tool for the revamping of a phosphate fertilizer complex. The use of recently emerged multi-software optimization tool is also explored as a way to enhance the engineering time dedicated to this problem

Progress in Applied CFD. Selected papers from 10th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries

Phosphate fertilizer plants are installations constantly evolving which make their design a challenging task. Phosphogypsum, a by-product of the manufacture of phosphoric acid, is piled up, forming stacks which may eventually alter the process efficiency as they encroach on process cooling ponds and locally modify the airflow fields. The easier access to high performance computing and the improvement of software capabilities allow to fully consider today the use of CFD within tight-schedule industrial projects, even the ones involving large-size geometry. As an example we describe how CFD can be efficiently used as a design tool for the revamping of a phosphate fertilizer complex. The use of recently emerged multi-software optimization tool is also explored as a way to enhance the engineering time dedicated to this problem.publishedVersio