Peter T. Luckie

Steady-state simulation of a cement-milling circuit

Abstract The conversion factor for specific rates of breakage, to change from results in a 200-mm diameter laboratory mill with 25.4-mm diameter balls, at Bond filling conditions, to a 4-m diameter production cement mill was found to be 2.75. The residence time distribution of the 10-m long, 2-compartment production mill was equivalent to 10 equal fully-mixed reactors in series, with a mean overall residence time of 5.58 min. A mathematical simulation of the mill circuit using experimental separator selectivity values gave a reasonably close match between simulated and experimental size distributions at various points in the circuit. The steady-state simulation model was used to predict how design schemes for different operation conditions would influence the product size distributions and output rates, assuming that the discharge diaphragm could be redesigned to preserve design mill filling conditions at different circulating loads. It was concluded that the increase of circuit output from the breakage view-point due to separation and rejects recycle was slight, and that improved separator efficiency to produce the same product would not result in significant increase in output, primarily because the size distribution of the finish product is close to that predicted from open-circuit operation.

Using Model Discrimination to Select a Mathematical Function for Generating Separation Curves

A statistical technique, known as model discrimination, is presented for selecting a mathematical function to fit separation data in order to estimate the characteristic parameters — the relative density of separation and the probable error. Some of the more commonly used functions are compared by their goodness of fit and their parameters evaluated statistically using a sensitivity analysis approach in order to determine the function with the best fit and the maximum parameter sensitivity. Application of this technique is demonstrated using sets of separation data from actual heavy media cyclone operations. For separator data exhibiting apparent bypassing, i.e., a fraction of feed apparently exiting with the clean coal and/or a fraction of feed apparently exiting with the refuse, a modelling technique is given whereby an existing function can be expanded to incorporate the bypass parameters.

The beneficiation of Martin Lake Texas lignite

Abstract Martin Lake lignite from Wilcox County, Texas, yields a moderate level of ash (11.3%) on combustion and has 13% inertinite macerals. These both act as diluents during liquefaction processing. A beneficiation process comprised of size selection, aqueous sulphur dioxide treatment and sink/float separation using heavy media was evaluated and shown to be effective. With laboratory scale equipment, the combined process gave a lignite product with 2.5% ash. A lignite recovery of 82% was achieved. In a commercial process the remainder could be used as plant fuel. Petrographic analyses of the various treated fractions were performed. The huminite (vitrinite) macerals were concentrated in the low gravity fractions whereas the inertinite was concentrated in the high gravity fractions. Owing to the association of the liptinite macerals with minerals, their distribution was bimodal with the highest contents occurring in both the high and low gravity cuts.

An Interpolation Methodology for Washability Data

A methodology for the interpolation of washabilily data is presented. This procedure provides a means whereby the washability data for both the weight and the attributes (e.g., ash, sulfur, etc.) can be interpolated for any size and/or relative density interval desired. Unlike some techniques which rely on the interpolation of interval values, this technique involves the interpolation of cumulative values. Since point values are used, there is no ambiguity as to what size or relative density corresponds to which interval value.

Application of an Unsteady-State Pulp-Partition Model to Dense-Medium Separations

Abstract Since there has been a growing interest in using gravity concentration techniques for the processing of fine coal (less than about 0.5 mm in size), it is important that a performance prediction procedure is used which is capable of showing differences in the operating conditions of the separator. The generation of fractional recovery or partition curves is one such procedure. A fractional recovery curve is a plot of the fraction of or probability that a given size feed material of a given density reports to the product against the density. This paper derives a mathematical model, based upon the physics of the separation process, from which fractional recovery values can be obtained. The heart of this derivation is the convection-diffusion equation which takes into account both the settling and the mixing of particles within a free-settling-type separator. The fractional recovery curve can be obtained by fitting these values to an appropriate mathematical function. Although the fractional recovery...

Towards a General Distribution Model for Flowsheet Design

Proper analysis of washability data can lead to the development of a maximum yield coal preparation plant flow sheet. Simulations, as simple as spreadsheet mass and water balancing, are important in examining yield maximization and middlings liberation. Key to such attribute tracking flow sheet simulations is the distribution model, expressing the probability of a species reporting to the product stream. There are many such equations proposed in the literature. This paper examines a functional form that can represent or fit most of the proposed distribution functions. Such a general function is very convenient in a general simulator, because the user need only define the relevant parameters instead of the appropriate equation and parameters.

Evaluating Coal Separation Processes

Abstract When evaluating the separation made by a coal cleaning device, particularly when examining new applications, it is important to have a procedure that is independent of the feed consist to the device and thus can show differences arising from various operating conditions. One such procedure is the generation of fractional recovery values, defined as the fraction of feed material in a given relative density interval for a given size interval which reports to the product, and the resulting curves. The methodology has been developed so that subjectivity on the part of the engineer is eliminated. This is achieved by first establishing a mass balance around the coal cleaning device, reconstituting the feed stream and then interpolating the feed and product streams into narrow size and narrow relative density intervals. Using these interpolated data, the fractional recovery values can be calculated and in turn fit to a mathematical function from which descriptive parameters, separation modulus, distribu...

Use of an Unsteady-State Pulp-Partition Model to Investigate Variable Interactions in Dense-Medium Separators

It would be convenient to study the effects of changes in operating conditions on solid-solid separations within a free-settling-type device with a mathematical model that takes into account the changes in the physics of the separation process. One such model, the unsteady-state pulp-partition (USPP) model, based on a convection-diffusion equation, can be used to generate fractional recovery values. These values give the fraction of or probability that a given size feed material of known density will report to the product stream. Furthermore, curves generated from these values can be described by certain characteristic operating parameters — the density of separation and the mean probable error. By examining the variation of these characteristic parameters with systematic changes in the model variables such as the separation time, separation efficiency changes can be investigated. In this paper, the USPP model is used to investigate the improvement in separation due to increasing the g-force and the role ...

Staged solid–solid separations revisited

Abstract Staging of separation operations to improve the overall efficiency of the process has always been practiced in mineral processing circuit design, be it cells in jigs, compartments in heavy media vessels or multiple cyclone installations. In fact, staging in circuit design occurs whenever a stream passes through a series of devices. However, the arrangement of the devices can affect the outcome across the spectrum of degradation, no improvement, improvement of the separation. Thus, it is critical to understand how the arrangement will affect the outcome. This paper presents a study of three general staging arrangements.

THE DEVELOPMENT OF COAL-BASED TECHNOLOGIES FOR DEPARTMENT OF DEFENSE FACILITIES

The third phase of a three-phase project investigating the development of coal-based technologies for US Department of Defense (DOD) facilities was completed. The objectives of the project were to: decrease DODs dependence on foreign oil and increase its use of coal; promote public and private sector deployment of technologies for utilizing coal-based fuels in oil-designed combustion equipment; and provide a continuing environment for research and development of coal-based fuel technologies for small-scale applications at a time when market conditions in the US are not favorable for the introduction of coal-fired equipment in the commercial and industrial capacity ranges. The Phase III activities were focused on evaluating deeply-cleaned coals as fuels for industrial boilers and investigating emissions control strategies for providing ultra-low emissions when firing coal-based fuels. This was addressed by performing coal beneficiation and preparation studies, and bench- to demonstration-scale emissions reduction studies. In addition, economic studies were conducted focused on determining cost and market penetration, selection of incentives, and regional economic impacts of coal-based technologies.