Investigation into Problems of Discharging Queensland Coals from Bottom Dump Rail Wagons

Coals from some Queensland mines cause varying degrees of difficulty due to hangup in rail wagons during unloading at the ports. Jackhammers are currently used at the ports to vibrate the wagons and initiate flow of the coal. Fieldwork, laboratory and pilot scale investigations have been conducted to identify the factors that contribute to the coal hangup problem and identify approaches to lessen its impact on the coal transport chain. Loading of wagons was identified as an important contributor to hangup in wagons and the position of first impact is of principal importance in determining the location of the consolidation in the wagons. Laboratory testing found that each coal has a minimum amount of loading force required to make it stick and additional loading force strengthened the arch formed near the hopper door outlet of the wagon. Train travel generated frequent (every few seconds) forces of 0.2 to 0.3 G and less frequent (every few minutes) forces of 2 to 3 G. Laboratory testing determined that the smaller travel forces did not cause further consolidation, but the less frequent larger travel forces further consolidated the coal. The central longitudinal tie bar in the wagon appeared to be an abatement point for arch formation and the consolidated coal needed to be removed to a height approximately 50 cm above the level of the tie bar in the wagon before achieving mass flow. The different coals formed arches of different strengths and hence required different amounts of jackhammering to break the arch. Pilot scale testing identified that the position on the wagon body affected the efficiency of coal removal and jackhammering of the front slope sheet of the wagon was more effective than jackhammering the side of the wagon. This testing also identified that jackhammer frequency affected coal removal and a frequency of 175 Hz gave best coal removal.