Coal Preparation

Application of X-ray Computed Tomography for Coal Washability Analysis

Coal Preparation » General

Published: October 13Project Number: C21050

Get ReportAuthor: Tuan D Nguyen, Anh V Nguyen, Chen-Luh Lin and Jan D Miller | The University of Queensland, University of Utah

Coal washability is currently obtained by float-sink analysis. The safety and technical concerns associated with the float-sink analysis due to the use of toxic, environmentally hazardous liquids have been recognized by the industry for many years. Moreover, this slow, time-consuming analysis must be conducted off-line in a lab and does not allow for developing an on-line coal washability analysis system needed for optimization and control of various unit operations in a coal preparation plant. This project aims to investigate the use of X-ray computed tomography (CT) to obtain the washability characteristics of coal. The CT-based coal washability analysis is non-destructive, non-toxic, fast and will allow for the development of an on-line coal washability monitoring system.


X-ray CT scanning techniques have been developed in the medical service field in order to provide internal images of the human body. The principle underlying CT scanning is the use of X-ray beam signals that are a function of the incident X-ray energy and the linear attenuation coefficient which relates to the local mean density of a small volume (voxel) within a particle. With the latest advances in X-ray CT hardware and software, computing power and the rapid cost reduction, the application of this technology in coal preparation becomes economically feasible. In this project we use the new high resolution X-ray micro CT (HRXMT) technology which combines the high-resolution 3-D X-ray micro-CT scanner and the specialised software to determine the composition and particle characteristics of coal samples with considerable details needed for building washability analysis.


Two coal samples taken from the feed streams to two DMC circuits at two different coal preparation plants in Australia were obtained, characterised and used in this project. The coal samples were fractioned into eight size fractions using sieves and eight density fractions using heavy liquids as per the Australian Standard AS 4156.1-1994. All the coal fractions were then used to determine the fraction-averaged densities using helium gas pycnometry and the total ash contents by massing the residue remaining after burning the coal samples under controlled conditions as per AS 4156.1-1994.


The XCT analysis of washability of the coal samples was conducted using the HRXMT scanners from Xradia. It involves packing the coal sized fractions into packed beds of coal particles which then were imaged using the HRXMT scanner, producing 2D images of cross-sections of the coal particle beds by rotating about the bed axis and translating perpendicularly to the X-ray beams. The 2D images were used to re-construct the 3D structures of the beds with known details about density and geometry of the constituted particles. The XCT analysis for 3D fine coal washability analysis of packed beds of coal particles involved two major next steps, namely, particle image segmentation and density measurement of individual particles to determine the particle-averaged density distributions and volumes of individual particles. These details were then integrated to build the washability curves for the given size fraction. Linear relationship between incremental ash versus reciprocal of density has been established for the Australia coal samples of different size fractions, and was used to calibrate the XCT-measured density and ash contents. The coal washability was successfully obtained using both the XCT technique and the conventional float and sink experiments. The coal washability determined by the XCT technique agreed with the washability obtained by float and sink analysis.


The objectives of the project were successfully achieved, namely:

· A methodology for the determination of washability data for Australian coals using XCT was successfully established and developed;

· The XCT instrumentation was successfully applied to obtain washability data and evaluate the technical feasibility of XCT for washability analysis of Australian coals;

· The XCT washability results were successfully compared and benchmarked with the conventional float-sink data which were obtained for the same coal samples following the Australian Standard AS 4156.1-1994.


The outcome of this project evidently shows that XCT can be used to perform coal washability analysis. XCT provides a new methodology for non-destructive and non-toxic determination of coal washability data. It is safe and fast. Therefore, XCT will allow for the development of an on-line coal washability monitoring system. It is recommended to expand the research activities into characterising breakage and washability of borehole samples for mine plan and processing strategy, and exploration prospect of new coal mines.



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