In this paper a project to develop a joint optimisation/simulation model for production planning in a mine-mill complex is presented. The system involves a mill receiving ore from a number of different locations, each with a unique mineral composition. The mill consists of several crushing and grinding circuits that function in series and parallel. Scheduling the fl ow of materials through the mill is complex due to constraints on throughput imposed by the mill’s design, the length of time material can be stockpiled on the surface, varying input mineral composition, and throughput targets for a range of output products. An optimisation model is used to create a set of campaigns (ore feed rates) over a given planning horizon under the assumption of deterministic mill throughput. A simulation model is used to evaluate the production plan under assumptions of stochastic machine failure and operational losses created by the need to cycle between input feeds. Campaign scheduling has two important implications for the simulation. First, during any campaign, multiple ore types may need to fl ow through the mill. However, the mill must be controlled to ensure that only one type of ore can be in a crusher, a grinder or a storage bin at any point in time. Second, as the mill switches from one campaign to another, the set of ores being processed may differ. Thus, the fl ow of ore through the equipment during a campaign changeover must be controlled to ensure that one or more of the ores from the current campaign can be completely eliminated before the ores from the new campaign are introduced. The simulation architecture employed for this project is Visual Basic for Applications (VBA) combined with MS-Excel as a user interface. A fi xed step discrete event orientation is assumed as the simulation framework. A set of model constructs was built for the project with a specifi c Canadian milling operation in mind, but was designed to be representative of a broad class of milling operations. The constructs are implemented as class objects within the VBA structure, each with a number of properties and methods. The collection of VBA objects forms a composable modelling toolkit. These objects can be linked together by users, via MS-Excel, to represent a broad range of milling operations.
展开▼
