Reduction of Carry-back and Coal Spillage in Rail Transport

Carry-back refers to material remaining within unloaded coal wagons on the return trip to mines, which has a negative impact on the Australian coal industry. Carry-back causes two problems: cross-contamination, and coal spillage.

Cross-contamination can adversely affect a coal supplier's reputation. Extraneous material within wagons carried back from a terminal, being mixed with higher quality coal at a loadouts may not be consistent with a mine's export specifications.

Coal spillage adversely affects the coal supply chain availability in three ways. Firstly, the cumulative affect of thousands of unloaded wagons leaking small amounts of remnant coal onto the track, contaminates the ballast, which can lead to derailments during wet seasons. Secondly, the combination of sticky coal and jammed-open kwikdrop-doors (KDDs), occasionally results in large-volume discharges and consequent derailments. Thirdly, managing coal hangups and spillage at dump stations, together with track possessions for ballast cleaning, reduces rail network availability.

This project has developed a carry-back detection system which is currently installed at RG Tanna Dump Station No 3. This system automatically generates alerts for control room operators whenever the volume of material residing within unloaded wagons exceeds a selected threshold. The carry-back information will serve to identify those wagons harbouring carry-back and which require intervention.

Small amounts of coal residing on leaky KDDs can be better managed by changing the closing trigger times. Wagons possessing large amounts of carry-back are currently subject to manual jack-hammering. Increasingly, large wagon vibrators are being employed to loosen coal hangups.

Surveys were conducted to quantify the carry-back. For the period March to August 2007, the average amount of carry-back was 0.36 tonnes per wagon. The factors that influence carry-back rates, include the mine, the wagon type and the season. In particular, for the two months after the torrential rains that occurred during June 2007, the carry-back exceeded 0.93 tonnes per wagon. That is, the equivalent of almost one wagon per train of sticky coal failed to be unloaded.

It is estimated that carry-back costs the coal industry in the range of $42M to $102M annually. Clearly, this justifies installing automatic carry-back detection systems and automatic wagon vibrators at the ports. The installation of automatic wagon vibrators should lesson the number of train reversals and improve cycle times. Containing coal within ports is arguably more efficient than cleaning up spillages and should contribute to improved network availability.