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A substantial research project on the performance of a 600 tonne per hour Batac jig involved removing large bed samples from four locations across the bed in the first compartment. The bed was sampled as four or more layers of constant thickness. In order to arrive at estimates of the continuous variation of bulk density and concentrations of particle size and density fractions with depth in a bed, a new method of interpolation, the basis of which is developed in the first paper in this series, was applied to the data. While it was not possible to determine trends in stratification with operating conditions of the jig, the work provided insight into bed stratification. A new jig bed stratification index was devised to quantify the state of stratification of the bed. The use of the interpolation method made possible the objective estimation of stratification.

Hughes’ has proposed a method for dealing with the problems of interpolating coal washability data which eliminates many of the difficulties encountered in previously proposed procedures. In particular, the problem of the interpolating function becoming negative was solved, but the computational procedure proposed was not suited to convenient computation. Lyman modified the solution to provide a smoother interpolating function, recast the computations in a manner well-suited to fully-automatic operation, and generalised and further extended the method to deal with a more difficult problem relating to interpolation of bulk density, size distribution and density distributions as a function of bed depth in samples taken from a jig bed. These methods were implemented in a major project by the author. This paper presents the mathematical background to both applications and provides an example of their application to simple interpolation of washability information. The second paper of this pair provides examples of the more complex application of the method to data arising from sampling a jig bed in layers, and the third paper considers two-dimensional interpolation of washability data.

The first paper in this series' presented the mathematical basis and computational procedures for problems of interpolation of sizing and density data commonly encountered in coal preparation problems. Robust methods having the desirable property that the interpolations reduce exactly to the original data were developed. This work discusses the application of the method to two-dimensional interpolation of size-by-size density and ash data. The primary application of the method is in consistently recalculating washability information to some chosen set of size and density intervals, given sets of data defined on a different set of intervals. Such a problem occurs when preparing drill core or bulk sample data for washery calculations. No ‘model’ of coal properties or assumptions regarding the forms of the mass or ash distribution are involved. The method is consistent, objective and computationally robust.coal preparation, Coal, density distribution, interpolation, size distribution, washability.

The jig in its variety of forms applied in coal preparation has been a major unit in coal washeries for one hundred years; yet the principles of jigging are still less well understood than those governing many other coal preparation unit operations. Jig control has also been viewed as an art rather than a science until recently. This review considers some of the history of jigs and the theories that have been advanced to explain their operation. Special emphasis is placed on discussion of the means of control of jigs, starting from the traditional means and working towards the novel methods that have been proposed recently. It is clear that our understanding of jigs and the means by which they will be controlled in the future will benefit from our rapidly increasing engineering computational power and will make much fuller use of microprocessor control and modern instrumentation.

Seven signals were accurately measured and data logged in exhaustive experiments using a highly instrumented and controlled pilot scale Baum jig. These signals provide a basis for understanding the effect of the operating parameters on the air and water behaviour in the jigging process. The measurements include the air pressure, water pressures and displacement, the hutch water flowrate. A Fourier decomposition method was applied to remove signal noise and smooth the signals. Water velocities and accelerations are calculated from the smoothed displacement data. The frequency of pulsation, air pressure in the accumulator and inlet period of the air cycle play significant roles in determining the air and water behaviour in the jigging process. The bed thickness. expansion period of the air cycle, hutch water flowrate and the rate of opening of the inlet valve are less important. The characteristics of four typical air cycles, namely, the conventional Baum jig cycle. Mayer cycle. Jeffrey/Bird cycle ...

To carry out washery optimization calculations in a digital computer, both the raw coal feed characteristics and separator efficiency performance must be reduced to a form that is both accurate and easv to translate into code. A systematic analysis has been made of mathematical representation for partition curves and separation characteristics for froth flotation machines. A number of representations of the partition curves have been found to be useful. The programs developed accept conventional partition data or modelled partition curve parameters. Flotation performance is specified according to a two-rate constant kinetic model. Feed coal characteristics used are typical for coal preparations plants in China. Optimization of the process is carried out by maximization of yield, and three programs have been developed for the purpose. The programs can deal with any one of seven plant flowsheets commonly used in China. One program can be applied to determine the optimal ash content of clean coal for either each category of separator or each coal feed group. The other two programs are very useful to determine the optimal cut points of separators being installed in a plant. The computing techniques applied in both the programs are the Rosenbrock pattern search and the so-called “Replacement Method”. The cubic spline interpolation techniques have been applied in a number of calculations with success. All the programs have been proved to be effective and convenient tools for the design and operation of coal preparation plants.

Models which have been presented in the literature consider only selected aspects of dense medium cyclone operation, are empirical in nature and generally relate only to severely limited ranges of operating parameters. This paper reports progress towards development of a more comprehensive and robust model. The data base consists of partitioning parameters developed using density tracers and conventional coal sampling and analysis techniques, together with recordings of parameters such as cyclone dimensions, feed pressure, medium size distribution and product media densities. These data were drawn from 15 Australian coal preparation plants. To eludicate the effects of important operating parameters on medium behaviour and on the partitioning of large particles a series of pilot scale tests were also conducted. The present model consists of eight sub-models which relate to particular aspects of dense medium cyclone operation such as medium flowrates and densities, or size-by-size separation densit...

The density tracer technique has for some years been utilised for determination of the separation efficiencies of density separators in the diamond and iron ore industries. At the Julius Kruttschnitt Mineral Research Centre (JKMRC), the technique has been adapted for studies of coal separation, and refined to a point where a Tromp or partition curve for a dense medium cyclone module can be determined quickly and accurately. Test programs using 33 mm tracers in seven Australian coal washeries are reported, and the effects of selected operating variables on separator performances are examined. The density tracer technique is shown to have substantial potential in improvement of day to day washery operation and the detection of unusual operating conditions, and in coal preparation research.

Systems for the routine on-line determination of ash content of process streams in coal preparation plants and handling systems have been in use in Australia for over four years. More recently, monitors for on-line moisture measurements have been developed to complement the ash measurement function. The technology for these systems is reviewed briefly. The development of reliable ash and moisture monitors has made the implementation of automatic systems of coal quality control practical. The emerging philosophies of automatic control in Australian preparation plants are examined with particular emphasis on systems involving dense medium circuit regulation. Related developments in flotation control and coal sorting are noted to complete this overview.

Density tracers are currently used in a large number of Australian coal preparation plants and research laboratories, yet few papers deal with the rigorous statistical treatment of the results from such tests. The numerical work described was carried out in order to evaluate the influence on the accuracy of derived partition data of the size of the specific gravity increment between adjacent tracers, and the number of tracers used per increment. It is shown that the sequence of tracers used in a test should be spaced at intervals not exceeding 2.5 times the expected separator E p in order to ensure that theE p is determined without bias. The influence of the number of tracers used at each specific gravity has been studied in terms of (i) the confidence intervals for individual tracer results, and (ii) the standard deviation of the cut point and E p determined when maximum likelihood estimation methods are used to fit a partition curve to the tracer results.