Improved stockyard management strategies for coal export terminals at Newcastle

Coal is Australia's leading export valued at close to A$50 billion and representing more than 20% of Australia's commodity exports in 2008 (Australian Department of Foreign Affairs and Trade). The Port of Newcastle is home to the world's largest coal export operation. In 2008, it achieved a throughput of around 92 million tonnes, or more than 10 per cent of the world's total trade in coal for that year. That throughput is expected to double in the next decade. Several coal terminals operate at the Port of Newcastle. Crucial to achieving a high coal throughput is effective management of the stockyards at these terminals. The stockyard, where cargoes of (typically blended) coal product are assembled in stockpiles using stacking machines, and then reclaimed using bucket wheel reclaimers, is a pivotal component of a coal export chain. In this paper, a model of stockyard operations within a coal export supply chain, with make-to-order cargo assembly, is described. Stockpiles are assembled from coal delivered by trains from load points at mines. For a given stockpile, it is known in advance how much coal must be delivered from each load point to completely assemble the stockpile. Trains arrive at a dump station and dump the coal onto a conveyor which transports it to a stacker which in turn assembles the stockpile on the yard. Once the stockpile is completely assembled (a process that usually takes several days), it is removed from the stockyard via a reclaimer and loaded onto a vessel (a process that usually takes around half a day to complete). A stockpile often remains in the stockyard for some time (several days) before its intended vessel arrives at the berth and it can be loaded. The system is constrained in a number of ways. There are limited berths available for vessels to be loaded. The departure of larger vessels may be restricted to high tide. Load point capacity at the mines, in terms of the number of trains as well as the volume that can be handled per day, is limited. Stockyard space is often at a premium, and dumping, stacking, and reclaiming capacity per day is limited too. All these constraining factors need to be taken into account when managing the sequencing and loading of vessels, and the management of the stockyard. The model developed represents decisions and constraints typically applied at a planning stage of about 4 to 6 weeks in advance. The key decisions are where on the stockyard to place each stockpile for a vessel, when to start building the stockpile, when to bring the vessel to berth, and when to start reclaiming and loading each stockpile for the vessel. An approximate railing plan for transporting coal from mine load points to the stockyard is also required, largely as a check on load point and rail capacity limits. The model considers the stockyard itself and the outbound handling in some detail, with timing at the hourly level, but approximates in-bound capacity constraints more coarsely, at the daily level. We give a solution approach, simulating stockpile placement and scheduling decisions in a greedy fashion, with the goal of minimizing vessel sailing delays, and maximizing throughput of the system. Since a greedy approach is unlikely to yield the most efficient schedules, a variant of the algorithm is developed in which the vessel scheduling order is randomized, and the resulting performance analysed computationally. The resulting model and algorithm together can be viewed as a prototype decision support system for the stockyard planner. However, it can also be used as a simulation tool, to explore the effects of alternative stockyard management strategies. Such strategies, may, for example, reserve some areas of the stockyard for fast-moving, and some for slow-moving, cargo, with the aim of balancing load across the stacking and reclaiming equipment. One such strategy is implemented in the model, and compared with the simple greedy approach. Computational results of this study are report. Our research shows that coal throughput can be substantially impacted by the stockyard management strategy employed.