Dense medium cyclones (DMCs) have become the workhorse of the coal preparation industry due to their high efficiency, large capacity, small footprint and low maintenance requirements. Although the advantages of DMCs make them highly desirable, size-by-size partitioning data collected from industrial operations suggest that DMC performance can suffer in response to fluctuations in feed coal quality. In light of this problem, a multi-stream monitoring system that simultaneously measures the densities of the feed, overflow and underflow medium around a DMC circuit was designed, installed and evaluated at an industrial plant site. The data obtained from this real-time data acquisition system indicated that serious shortcomings exist in the methods commonly used by industry to monitor and control DMC circuits. This insight, together with size-by-size partition data obtained from in-plant sampling campaigns, was used to develop an improved control algorithm that optimizes DMC performance over a wide range of feed coal types and operating conditions. This document describes the key features of the multi-stream monitoring system and demonstrates how this approach may be used to potentially improve DMC performance. / Master of Science

Dense medium cyclones are used extensively in the mineral processing industry to beneficiate various minerals including coal, diamonds and iron ore, amongst others. According to Reeves (2002), .the cyclone has been installed in over one-quarter of the coal preparation plants worldwide.. Dense medium cyclones have the ability to achieve high capacities, and simultaneously obtain sharp separations and high separation efficiencies. However, this piece of equipment does have a shortcoming in that its capacity is constrained by the solids carrying capacity of the spigot. This is termed the spigot capacity. There is uncertainty on whether the spigot capacities specified by DSM (Dutch State Mines), the original developers of the dense medium cyclone, can be increased or not, and how these capacities were determined. The purpose of this study is to establish a methodology to determine the spigot capacities of dense medium cyclones, and determine the parameters that influence these capacities. In order to illustrate the significance of increasing the capacity of dense medium cyclones, the following coal example is used: In 2005, South Africa produced about 245Mt of coal valued at R35.86 billion. A significant proportion of this coal is beneficiated through dense medium cyclones. Therefore, an increase in the cyclone capacity, even if relatively small, represents a large number in terms of tonnages of coal produced or monetary gains. It has been established clearly in this investigation that the maximum spigot capacity is reached at the onset of roping. A critical sinks ore concentration at which spigot overloading occurs has been observed. The simplest and best indicator of possible spigot overloading has been established to be the sinks ore concentration, measurement of this parameter could, however, prove challenging on most industrial cyclones. Further, spigot overloading of a dense medium cyclone can be detected visually by observing the discharge type at the sinks and monitoring particle misplacement to the floats stream. A regression model that quantifies the spigot capacity, in terms of ore and slurry, has been developed. Various parameters were considered in the model, these include: cyclone geometry, feed head, medium density, and medium grade. Parameters that influence the spigot capacity of dense medium cyclones have been established, and their effect on the spigot capacity has been quantified. The spigot capacity values obtained in this investigation were compared with those specified by DSM, and it was concluded that there is large potential to increase the .spigot capacities. specified by DSM. / Dissertation (MEng (Metallurgical))--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

Dense medium separation (DMS) plants are typically used to beneficiate run-of-mine (ROM) coal in coal metallurgy. These plants normally make use of a dense medium cyclone as the primary processing unit. Because of the deviations in the ROM quality, the production yield and quality become difficult to maintain. A control system could benefit such operations to maintain and increase product throughput and quality. There are many different methods for developing a control system in a metallurgical operation; however, what is most fundamental is the use of a mathematical model to design a controller. For this reason, a first principle dynamic mathematical model has been developed for a DMS circuit. Each unit operation is modelled individually, then integrated together to form the complete system. The developed DMS circuit dynamic model is then used to simulate the process. It is also found that most models developed for DMS operations typically make use of steady-sate analysis and that very little literature is available on dynamic models of this kind. Difficulties that arise when validating a model in metallurgical processes are insufficient measurement points or the challenges in measuring certain variables, such as physical properties (e.g. particle size) or chemical components (e.g. ash percentage). This paper also explains how the Runge-Kutta approximation can be used in simulating DMS unit processes with intermediate online measurements that may be available. This can ultimately assist in verifying the accuracy of the simulation. One of the other problems that can occur when developing models from first principles is the estimation of model parameters. Specifically when non-linear state-space relationships are developed, one must ensure that there is a unique solution for the parameters in question. A method employing parameter identifiability is also presented in this dissertation to illustrate its use. In addition the process of estimating parameters is explained and illustrated. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

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