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Coal Preparation

Improved Washability Prediction Through Establishment of Correct Coal Size Distributions

Coal Preparation » General

Published: June 98Project Number: C5053

Get ReportAuthor: Andrew Swanson, I Fletcher, W Membrey, R Davis | Quality Coal Consulting, ACIRL, Mining and Exploration Geology Services

The prediction of coal size distributions during the process of mining, handling and preparation are of great importance in preparation plant design because of the need to adequately cater for appropriate amounts of fine coal, and to be able to provide realistic samples for washability determinations. The results from an earlier NERDDC-funded size distribution project (Swanson et al 1993) are summarised, and further studies have been undertaken into the development of a pretreatment procedure for borecores and strip samples to generate more reliable coal washability data by better prediction of size distributions.

Samples of run-of-mine coal, strip samples and large diameter core samples from the same small block of coal have been collected from two sites in New South Wales and Queensland. These samples have been used to examine and refine processes which are part of sample pretreatment procedures for the generation of samples with sizings that predict plant feed size distributions.

The drop shatter process has been refined. A mechanical device has been designed and constructed to improve the reliability and efficiency of the test, and testing has confirmed that it provides reproducible results. Experiments have shown that sample mass is not a critical factor in the drop shatter, dry tumbling or wet tumbling of samples between 7 kg and 50 kg. A new calculation method has been developed to determine drop shatter end-points, replacing the reliable, but difficult to perfect, graphical technique. Abrasive breakage, the rubbing together type of breakage, has been examined, and on balance a dry tumbling time of 3 minutes appears to provide appropriate fines generation. Test samples have been crushed in industrial sized low speed, high torque crushers, and the use of a choke-fed jaw crusher has been shown to provide a suitable simulation of these crushers for top size reduction. The wet tumbling process to simulate the breakdown of water-degradable clays and minerals has been examined and procedures to handle samples of less than 50 kg have been confirmed.

The pretreatment of non-seam material, such as roof and floor, has been studied, and samples have been given exactly the same treatment as the adjacent seam sample.

There was no evidence to suggest that large diameter core samples require any special handling or treatment.

The number of drops equivalent for various items of raw coal handling plant as determined in the original NERDDC study (Swanson et al 1993) has been reviewed and updated in the light of fresh data obtained since that project was completed.

The full pretreatment procedure has been thoroughly documented, and will be presented for consideration for issue as an Australian Standard.

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