This reliability model illustrates a typical closed circuit grinding mill circuit, used in many mine processing plants.
3 mills are installed, and the process requires at least 2 online at any one time to maintain required flowrate. The flows through each mill are also cycled to equalise the circuit outputs over time.
Extensive planned shutdowns are required, and while the PM's are timed to occur at regular frequencies, precedence conditions for each PM trigger prevent more than 1 mill being offline (i.e. the PM will wait until there are at least 2 other mills online before triggering).
Some failure modes are included in various items of equipment to illustrate the effects. The predominant shutdown driver in this model is the planned maintenance events. (Note : most mill circuits will require far more than the PM's shown, the quantity and frequency shown is for illustration ONLY).
The model has been purposely arranged to show reliability elements (equipment) and flow circuits separately. There is no reason these cannot be combined for simple circuits like this however - this is more to allow the flow model to be easily followed and debugged.
Linking the flow elements to either individual items of equipment (or simply the last element in the circuit in this case) allows the model to calculate flows and interruptions caused by equipment stops. The primary reason for doing so is to link the circuit outputs in terms of product, rather than a straight machine availability number. Since flow is provided to only 2 mills at any one time, the actual machine availability is not a true representation of the equivalent plant output - unless the PM's and failures reduce average mills online to below 2 out of 3 (in this case the average mill qty available is > 2.8 out of 3).
The flow circuit can also be designed to adapt to abnormal equipment operations - the in-built design margins can be used if there are less than 2 mills in operation (i.e. maximum flows are invoked whenever minimum online requirements are breached). The selectors in the data input container are used to check the number of mills online and then set the flowrate. This is a key difference between RBD type availability models and flow capacity models - in this case some increased flows can be called up to minimise the effects of below minimum equipment requirements.
The model uses dashboards above to allow user inputs and results to be easily manipulated. The dashboards also allow the sensitivity of the model to be seen immediately by altering selective inputs.
The results screen has direct links to selected equipment status histories to allow easy client interaction.