P. N. Holtham

On-line analysis of froth surface in coal and mineral flotation using JKFrothCam

The personal computer revolution has resulted in the widespread availability of low-cost image analysis hardware. At the same time, new graphic file formats have made it possible to handle and display images at resolutions beyond the capability of the human eye. Consequently, there has been a significant research effort in recent years aimed at making use of these hardware and software technologies for flotation plant monitoring. Computer-based vision technology is now moving out of the research laboratory and into the plant to become a useful means of monitoring and controlling flotation performance at the cell level. This paper discusses the metallurgical parameters that influence surface froth appearance and examines the progress that has been made in image analysis of flotation froths. The texture spectrum and pixel tracing techniques developed at the Julius Kruttschnitt Mineral Research Centre are described in detail. The commercial implementation, JKFrothCam, is one of a number of froth image analysis systems now reaching maturity. In plants where it is installed, JKFrothCam has shown a number of performance benefits. Flotation runs more consistently, meeting product specifications while maintaining high recoveries. The system has also shown secondary benefits in that reagent costs have been significantly reduced as a result of improved flotation control

A review of CFD modelling for performance predictions of hydrocyclone

Abstract A critical assessment is presented for the existing numerical models used for the performance prediction of hydrocyclones. As the present discussion indicates, the flow inside a hydrocyclone is quite complex and there have been numerous numerical studies on the flows and the particle motions in hydrocyclone, with a wide range of turbulence and multiphase models tested. Two-equation k-ε and RNG k-ε models flow velocities with empirical modifications were led to poor results, especially the tangential components in comparison with experimental measurements. Most of the recent studies have utilized the Reynolds stress models (RSM) with different degrees of complexity in the pressure-strain correlation. These RSM studies showed good agreements with velocity measurements. Unfortunately, the velocity profiles were not validated in most of the RSM cases where multiphase particle tracking were applied. Finally, large eddy simulation (LES) is the most advanced turbulence model applied in recent hydrocyclone numeric studies. Besides the additional information on précising the air core correctly, LES provides an additional accuracy in predicting the velocity profiles or the grade efficiency in comparison to the RSM. The multiphase models have been successfully applied in a hydrocyclone to model the Lagrangian motions of spherical particles. Eulerian-Eulerian model have been used to account for the particles effect on the fluid viscosity. Simplified Eulerian model (mixture) model predictions for solid transportation in cyclone were well predicted. Further, the inclusion of modified slip velocity calculation in the Mixture model improves the efficiency predictions close to the experimental data at low feed solid loadings. In future studies, the focus should be to model the three-dimensional flow in a hydrocyclone using at least the Reynolds stress model/LES. The particle tracking should at least include the effects of the turbulence on the particles. All these developed models will only applicable to low feed solid concentration levels. Since most of these models neglect the particle-particle interactions, a more comprehensive numerical method of modified Mixture model is applied for simulating solids flow in hydrocyclones for high feed solids concentration. Explicit models for accounting hindered settling and turbulent diffusion investigated for high feed solid concentrations in industrial cyclones are encouraging.

The particle detachment process in flotation

Experimental measurements of particle-bubble detachment forces by means of a novel vibration technique provide a more realistic analogue of the conditions in a flotation cell than the centrifuge techniques previously adopted. The detachment forces measured using the new apparatus show good agreement with the forces predicted theoretically by Nutt. The amplitude of any oscillations imposed on the bubble is found to be the dominant factor in the detachment process.

A Review of Flow Modeling for Dense Medium Cyclones

A critical assessment is presented for the existing fluid flow models used for dense medium cyclones (DMCs) and hydrocyclones. As the present discussion indicates, the understanding of dense medium cyclone flow is still far from the complete. However, its similarity to the hydrocyclone provides a basis for improved understanding of fluid flow in DMCs. The complexity of fluid flow in DMCs is basically due to the existence of medium as well as the dominance of turbulent particle size and density effects on separation. Both the theoretical and experimental analysis is done with respect to two-phase motions and solid phase flow in hydrocyclones or DMCs. A detailed discussion is presented on the empirical, semiempirical, and the numerical models based upon both the vorticity-stream function approach and Navier–Stokes equations in their primitive variables and in cylindrical coordinates available in literature. The existing equations describing turbulence and multiphase flows in cyclone are also critically reviewed.

Investigation of Recently Developed Monitoring Instruments for DMC Circuits at New Acland

The objective of this Australian Coal Association Research Programme (ACARP) supported project was to bring together at a single site the two research groups involved in dense medium cyclone (DMC) instrumentation and software development to demonstrate the following: the long-term capability of the instruments in a coal preparation plant environment, a comprehensive DMC monitoring and measurement reporting capability, and the application of smart sensors to maximize the utility of measurements of this nature. The instruments were deployed for a minimum of 12 months and, apart from some initial issues, were shown to operate effectively in the robust environment of an operating plant. These instruments included motion analyzers on the desliming, product and reject drain and rinse screens, electrical impedance spectroscopes (EIS) for measuring the medium densities of the correct, DMC feed, overflow and underflow streams, a through tile density meter, and in-stream density meter provided measurements of the amount of magnetite in the medium at the DMC vortex finder and underneath the product drain screen. The motion analyzers were calibrated to link the stroke of the screens with the tonnes per hour of the oversize stream reporting from the screens. This meant that the mass flow of feed to the DMC and the product and reject streams was now available dynamically. From this data, an estimate, for the first time, of the on-line yield could be calculated.

OPTIMISATION AND CONTROL OF DENSE MEDIUM CYCLONE CIRCUITS

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of Queensland’s Julius Kruttschnitt Mineral Research Centre (JKRMC) have conducted a number of Research projects focussed on the Dense Medium Cyclone (DMC) circuit in coal preparation plants. Research covered areas such as screen optimisation, drain rates of multi-sloped screens, medium quality and the effect of medium quality on the DMC operation. These projects have led to the development of instruments and techniques to measure the aperture and open area of screen decks, stroke and screen motion and the DMC overflow and underflow medium densities. This has provided researchers with a unique opportunity to investigate the factors that control the efficiency of DMC operation, and to determine control strategies to optimise the DMC process with particular emphasis on the underflow and overflow medium densities as an indicator of DMC and correct medium “health”.