Investigation of Factors Which May Be the Cause of Flow Problems During Discharge From Rail Wagons

This report provides details of an investigation of the causes of "sticky coal". It includes a series of laboratory tests conducted to explore coal characteristics, review of mine site operational procedures, and laboratory tests on wagon loading procedures, which may be contribute to flow problems during discharge from rail wagons, the cause significant and costly rail unloading delays.

Tested coal types are:

· Coal B - Coking coal - Queensland

· Coal C - Thermal coal - New South Wales

· Coal D - Hard coking coal - Queensland

· Coal E - PCI coal - Queensland

The coal types have problems with discharge from coal wagons on arrival at the relevant Port Terminal, resulting from coal "sticking" to the sloping surface of wagons, and arching over wagon doors.

New coal sampling procedure

Coal D and coal E samples were collected at DBCT rail receival direct from wagons with unloading problems caused by sticky coal. The new sampling procedure was arranged by Mark Van Moolenbroek on behalf of DBCT Pty Ltd. This is an important new procedure, providing coal sample with specific sticky coal characteristics, thereby overcoming previous unreliable test outcomes due to non-representative sample material.

The Study has included the following research:

· Chemical treatment to reduce clay content

· Reduction in ultra-fines content to reduce coal stickiness

· Relationship between coal flow properties and moisture content

· Review of train unload time

· Effect of rail wagon loading procedure on sticky coal and unloading delays

· Mine site operational procedures

The Project has addressed key issues nominated in previous ACARP Reports, and has conducted focused research with outcomes providing operational procedures capable of implementation.

Untreated coal with sticky coal characteristics, when subjected to ECT testing, have shown that the measured cohesive strength is approaching the "handling issues probably will occur" zone. Application of "another influence" would almost certainly increase the cohesive strength into the "handling issues probably will occur" zone, or even to the "handling issues most likely will occur" zone.

This report proposes that 'another influence' is the consolidation by impact of the sticky coal with the wagon surface during the initial stage of wagon loading operation.  

It may be concluded that contributing factors to sticky coal flow problems are cumulative and progressive, over three basic stages.

1. Product's "as mined" sticky coal characteristics

· Fines content

· Inherent moisture

· Free moisture

· Ash content

· Clay content

2. Mine site operational factors

· Fines increase by handling operations

· Production moisture addition

· Stockpile residence time factors

· Rainfall moisture addition

3. Wagon loading procedure

· Coal drop height

· Impact with wagon surface

· Wagon design

It is recommended that the above conclusion should form the basis of further research and recommended action to minimise effects of sticky coal wagon discharge problems.

To address sticky coal flow problems it is important to understand the relative importance of each factor, and the progressive cumulative effect.

It is important to recognise the difference in characteristics of coal types. It is recommended that "as mined" sticky coal characteristics, mine site operations, and modified load procedure, should be further investigated for a broader range of coal types.

It is recommended that all future sticky coal samples for test and research purposes should be obtained from coal in wagons when discharge problems are evident, to maximise relevance of outcomes and cost effective recommendations.

It is likely that the most cost effective solutions to wagon discharge problems could be found in changes to mine site operational procedures, and modified wagon loading procedure.

Previous successful field trial of the modified wagon loading procedure, supported by recent successful laboratory simulated wagon loading tests with undisputedly sticky coal samples, confirm the success of the procedure in improving rail wagon coal discharge.

It is recommended that Coal Producers whose products cause wagon unloading delay should be encouraged to undertake field trials of the proposed modified wagon loading procedure.

The earlier trial of modified wagon loading procedure still achieved an effective wagon load profile and full wagon load, but some fine tuning of the modified procedure may be required to suit individual loading facilities.

It is recommended that effectiveness of DuPont wagon spray product be investigated.

As fines content is a major coal characteristic contributing to sticky coal wagon discharge problems, further investigation of fines reduction chemical solution options should be conducted. Reduction in coal fines also achieves improved management of dust emission and may have other commercial benefits.