G.T. Adel

A study of axial mixing in column flotation

Abstract Pulsed tracer tests have been conducted to quantify the effect of physical variables on axial mixing in column flotation. The tracer studies were used to determine the residence time distribution (RTD) for different column geometries and operating conditions. For each test, the Peclet number and mean residence time were determined from the RTD data. Based on these results and industrial test data, a dimensional analysis approach was taken to develop an expression that relates Peclet number to column geometry and operating variables. Using this expression, it is possible to estimate the scale-up factors, in terms of retention time, that are necessary to account for increased mixing in larger columns.

Effect of operating parameters in stirred ball mill grinding of coal

Abstract For any physical separation process to work efficiently, a high degree of liberation must first be achieved. In the case of coal, a mean particle size as fine as 5 μm may be necessary when deep cleaning is required. One of the most energy-efficient devices for producing micronized coal is the stirred ball mill In the present work, various operating parameters such as stirring speed, pulp density and the use of grinding aids have been studied using a laboratory stirred ball mill. It has been found that the mill operates most efficiently at low stirring speeds and high pulp densities, as long as the viscosity is controlled within limits. The use of grinding aids reduced the energy consumption significantly, which may be attributed to a reduction in slurry viscosity.

Liberation modeling and parameter estimation for multicomponent mineral systems

Abstract A mathematical model has been developed to simulate the size reduction/liberation behavior of complex ores for the cases of batch and open-circuit continuous grinding. As compared with other models of this type reported in the literature, this one is absolutely free from restrictions on the number of mineral components and composite particle classes which can be represented. A modified Levenberg—Marquardt algorithm and a finite difference Jacobian are used in conjunction with the model equations to estimate all kinetic parameters. The estimation scheme is validated for a binary ore with five composite particle classes, while the model is used to simulate the liberation behavior of a ternary ore with five composite particle classes for each composite type.

Liberation modeling using automated image analysis

Abstract A population balance model describing the combined processes of size reduction and mineral liberation has been developed for batch grinding. Important model parameters including breakage distribution functions, breakage rate functions, and liberation functions have been determined experimentally by examining the mill product using a Zeiss SEM-IPS image analyzer. Areal assays, obtained from image analysis of monosized particle mounts, have been found to correspond quite closely to the actual chemical assays. As a result of the model parameter analysis, breakage distribution functions have been found to be independent of the grinding environment, while breakage rate functions appear to be sensitive to it. The model has been validated by simulating the batch grinding of a sphalerite ore from Tennessee. Excellent agreement between the model predictions and the experimental results is observed for both monosized and multisized feed materials. The liberation function has been found to be useful for analyzing the liberation mechanisms of composite particles.

Scale-up and design aspects of column flotation

ABSTRACT Recent interest in the commercial application of column flotation has led to a need for scale-up and design procedures which can be applied to this technology. A review of the literature indicates that operating parameters and column geometries can vary greatly from one installation to another. In this investigation, a salt tracer technique has been used to study the mixing characteristics of several bench-scale flotation columns. This information has been combined with data from the literature to develop a scale-up procedure for determining the column dimensions required to achieve a given throughput. The results of this investigation indicate that mixing within the column does not vary greatly over the wide range of column geometries commonly encountered in commercial operations.

POC-SCALE TESTING OF A DRY TRIBOELECTROSTATIC SEPARATOR FOR FINE COAL CLEANING

The project has reached the point where the Proof of Concept (POC) electrostatic separator is in the design stage. During the quarter, the design concepts of the TES unit have been finalized with Carpco. During the past quarter, most of the personnel assigned to this project have been performing work elements associated with process/engineering design (Task 3) of the process including the TES unit, the Turbo charger and the product conveying system.

In-plant testing of microbubble column flotation

A project to evaluate the performance of the Virginia Tech Microbubble Column Flotation (MCF) process in an operating coal preparation plant was initiated during this past quarter. The project is concerned with the collection of process operating data using a 30-inch diameter column, and using this data to scale-up to a prototype, full-scale plant column. The work is being carried out at the Marrowbone Preparation Plant owned by the Shell Mining Corporation. Work has primarily concentrated on finalizing the project work plan (Task 2.1 -- Project Planning), instrumenting the 30-inch diameter column (Task 2.2 -- Advanced Instrumentation) and conducting a preliminary parametric study to evaluate the performance of the column (Task 2.3 -- Detailed Testing). To date, the column has been consistently capable of producing a 9.5% ash product at a 61% combustible recovery from a -150 mesh classifying cyclone overflow containing 55--60% ash at 3--5% solids. Tests conducted over an extended period of time indicate that the column consistently maintains grade in spite of fluctuations in the feed characteristics. 12 figs.

The Assessment of Fine Coal Cleanability

ABSTRACT The ultimate cleanability of a coal by a physical separation process is dictated by its washability. In general, coal washability improves as particle size is reduced. Unfortunately, standard methods of accurately determining fine coal washability have not yet been established. In the present work, washability data for 28 mesh × 0, 200 mesh × 0, and 20 µm × 0 Pittsburgh No. 8 coal are obtained and compared using three different experimental characterization techniques. These techniques include image analysis, centrifugal float-sink analysis, and flotation release analysis. The image analysis and centrifugal float-sink techniques are found to produce similar washability results since these techniques are governed by the bulk properties of the coal. Release analysis, on the other hand, is governed by the surface properties of the coal and always produces an inferior separation. The results of the present work strongly suggest a need for developing improved gravity separation techniques for processing fine coal.

POC-scale testing of a dry triboelectrostatic separator for fine coal cleaning

It is the objective of the present project to further develop the triboelectrostatic separation (TES) process developed at the Federal Energy Technology Center and test the process at a proof-of-concept (POC) scale. This process has a distinct advantage over other coal cleaning processes in that it does not entail costly steps of dewatering. The POC-scale unit is to developed based on (1) the charge characteristics of coal and mineral matter that can be determined using the novel online tribocharge measuring device developed at Virginia Tech, and (2) the results obtained from bench-scale TES tests conducted on three different coals. At present, the project is at the stage of engineering design, which has three subtasks, Charger Tests, Separator Tests, and Final POC Design. Work accomplished during the current reporting period pertains to the first two subtasks.