Towards Better Fine Coal Classification

It is well recognised that the efficient classification of fine coal in the range of 0.04 - 0.3 mm is a key technology area to improve the efficiency of coal preparation. ACARP has invested substantially in the area of fine coal classification, and in order to maximise the benefits of past projects, an initial part of this project was to summarise the findings from completed projects, to understand the shortcomings, conduct a wider literature survey and distil the relevant findings as a basis to move forward on. Generally, this project aimed to better position the industry with respect to understanding the current state of the art with respect to fine coal classification, and to identify future areas for research efforts. Discussions with suppliers and operators indicated there is a great deal of interest in this area.

Cyclones are at the heart of all fine coal classification and there has been few advances in this area, apart from improved modelling some 15-20 years ago. There looks to be no blue sky technology improvements in this area, and so there should be a renewed effort to model cyclone performance, especially in light of variable feed conditions, to improve application engineering and plant control methodology. Improved on-line instrumentation and timely, reliable analyses of process streams would be of great benefit to plant operators and OEMs alike.

As part of the project, representatives from vendors and plant operations were approached to discuss the current and future state of fine coal classification. Questions covered the most appropriate technologies, key challenges, future developments, and where research should be focused. Across both groups, there was a general view that using large diameter, low pressure cyclones was a poor choice, that minimised capital and operating costs at the expense of process efficiency.

Sievebends were generally acknowledged as the current industry leader for performing larger cutpoints, although a number of the plant operators expressed challenges with the maintenance requirements. There was significant interest in technologies like the Derrick Screen to address some of these shortcomings. The variation in feed quantity and quality was identified as a key challenge in fine coal classification, especially as hydrocyclone performance and cutpoint are strongly influenced by the feed characteristics.

To develop a value proposition for further R&D into the fine coal classification, it is necessary to understand how sensitive total plant yield is to variations in classification efficiency and circuit configuration. A desktop analysis has been undertaken using Limn: The Flowsheet Processor, to estimate the impact of hydrocyclone performance, and alternative fine coal classification configurations, on plant yield for a constant ash. Two CPP configurations were considered, a typical Hunter Valley DMC/spirals plant and a typical Queensland DMC/spirals/flotation plant. Six feed samples were used as the basis of the study, three from Queensland and three for NSW, and three of the samples were considered to have high levels of ultrafine clays, while three were considered to have low levels of ultrafine clays.

One of the objectives of the project was to provide a framework for plant operators and designers to make the best choices for fine coal classification equipment/installation. The survey results and simulation outcomes describe the issues to be considered when considering different fine coal classification duties.