Graham O'Brien

Coal characterisation by automated coal petrography

Automated imaging techniques were refined to characterise the rank and maceral composition of coals by a full maceral reflectogram of polished coal grain mounts. Precision was improved by processing individual grains in each image separately and correcting within the software for the topography that occurs between the different macerals and minerals in the grains. Maceral group proportions and vitrinite reflectance information extracted from these reflectograms compared well with manual results for a comprehensive suite of Australian coals varying in rank from a mean vitrinite reflectance of 0.48-2.13%. A parameter that combines rank and type calculated from the reflectograms correlated strongly with chemical properties determined by ultimate and proximate analyses. For a limited number of samples, for which coking tests had been performed, this parameter also correlated with estimated coking performance. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.

The Application of the Coal Grain Analysis Method to Coal Liberation Studies

Emerging coal markets such as the use of coal for conversion to liquid fuels and its use in fuels cells and as coal water slurries in diesel engines require coal products with different coal quality specifications than those applicable to traditional coal markets of coke making and conventional power generation. As well as quantifying coals in terms of their chemical and physical properties, detailed knowledge of the mineral inclusions within the coal particles is required to identify coals that are suited to economically produce the low-ash value coals required for these markets. Hence, it is necessary to understand the associations of the minerals and macerals in individual particles as these give a particular coal not only its chemical attributes and utilization performance but also its washability (density distribution) and contribute to its surface chemistry characteristics. These attributes pinpoint the coals that are suited to beneficiation techniques that can be employed to produce economic amounts of low-ash value products for these new markets. After mining and processing, some particles can consist of essentially pure components of a single maceral or mineral phase whilst others are composite particles that are comprised of varying amounts of macerals and minerals. The proportion of particles that are present as pure components or as composites will be a function of the characteristics of the coal and the particle size. In general, it is considered that size reduction will result in liberation and hence increased yield. The amount of liberation that occurs during crushing or grinding a coal is however coal specific. Particle characterization information provided by an optical microscopic-imaging method, Coal Grain Analysis, was used to identify coals that might benefit from additional crushing to improve recovery of clean coal by new density separation techniques and by flotation. As expected, the results of these studies suggest that the degree of liberation that is obtained is coal specific, and, hence, yield improvements are also coal specific. Hence a quantitative method of investigating this issue is required.

The Use of Tri-Block Copolymer Surfactants as Promoters to Improve Flotation Recovery of Poorly Floating Coal Components

The use of tri-block copolymer surfactants as flotation promoters to enhance the recovery of poorly floating components of coal is examined. Previous study of the flotation response of different coal components using the coal grain analysis tool showed that coarse particles of inertinite, inertinite-rich, and vitrinite-rich composites were poorly recovered compared with liberated vitrinite. Improved recovery of these poorly floating components by using targeted reagents could boost the saleable product coal and, hence, economic outcomes. This approach requires only minor modifications to existing fines circuits. The reagents used were surfactants from the group of tri-block copolymers of polyethylene oxide/polypropylene oxide. The tests were complemented by the coal grain analysis tool that allowed the impact of the reagents on the recovery of the problem components to be properly assessed. Laboratory and full-scale flotation experiments were conducted by adding small amounts of the promoters before adding conventional collector (diesel). Flotation recovery was significantly increased with only a small product ash penalty in each case. Coal grain analysis showed that recovery was improved for most components, especially the coarse composite grains.

Optical microscopy as a new approach for characterising dust particulates in urban environment

In urban environments airborne particulates (dust) must be managed to ensure that industry and community coexist in a mutually beneficial and sustainable manner. The composition of the dust is a function of the local environment and industry. In general, there is a view by many community members that a significant proportion of inhalable (PM10) and respirable (PM2.5) dust in these environments could be coal. Thus there is a need to have an analytical method that provides a quantitative analysis of the amount and size distribution of the different particulates that can be present in air samples. Australias national research body, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has developed a Coal Grain Analysis (CGA) system that uses reflected light optical microscopy to provide a unique visual perspective, a qualitative feeling of the sample and quantitative information on the composition and size of the individual particles greater than 1 μm. Furthermore, semi-automated Optical Dust Marker software uses each individual particles colour reflectance fingerprint to classify that particle. These markers can currently identify coal, combustion chars, iron, quartz/dark minerals, pyrite/bright materials and particulates of organic origin. This paper presents a case study performed using CGA to evaluate the dust composition and proportion of coal and other particulates and also their size distribution in samples collected in an urban area along a coal rail corridor in Newcastle (Australia). In coastal environments a significant proportion of dust can be water soluble (salt) particulates; the proportion of soluble particulates in those samples varied from 46% to 52.3%. The concentration of insoluble particles in samples varied from 5.9 to 15.5 μg m-3 in the PM2.5-10 fraction and from 0.4 to 0.9 μg m-3 in the PM1-2.5 fraction. All samples consisted predominantly of particles of organic origin (mostly plant and insect remains) - 55.3%-85.3% by mass. Dark material particles of mainly inorganic origin (low reflecting material, mainly stone dust, clay, soot, rubber and soil), combustion char and metal particles (rust and iron oxides) were present in lower concentrations - 0.0% to 19.9% by mass. The amount of coal in the water insoluble fraction of the samples ranged from 5.3% to 19.7% by mass with 2.9%-13.5% by mass of coal particles in the thoracic (2.5-10 μm) and 0.3%-1.2% by mass in the respirable (1-2.5 μm) size fraction.