The digital model is the foundation element of the digital twin—a computerised simulation of a physical object or a proposed object to be designed in conceptual development. There is no automatic data exchange between the physical object and the digital model. As the physical object’s data is not integrated with the digital model, any changes made to the physical object are not represented in its digital model. The digital model requires input data to calculate and simulate the outputs. Typically, this input data is based on first principles, synthetic or hypothetical data, manually derived using assumptions or historical data. There are two types of digital models used in process plant simulations: steady-state and dynamic simulation.
Steady-state simulation
Steady-state simulation modelling is used for process design and evaluation. It is based on first principles such as conservation laws and thermodynamics. Design conditions are manufactured and not always achievable due to real-world changes in raw materials, product specifications, and the inherent dynamic behaviour of process over time. Steady-state assumes that input variables are constant with respect to time, and there is no time-lag dependency or accumulation in the process where input is assumed to equal output.
Dynamic simulation
While dynamic simulation models are also based on first principles, additional variables are applied such as kinetics. Unlike steady-state, dynamic modelling considers the mass and energy rate of accumulation within the process and calculates the time-lag dependency. It is the best modelling tool to capture transient conditions, real-time behaviour and batch and semi-batch processes. A digital twin for a mineral processing plant must contain the foundation block of a digital model that has been built using dynamic simulation to reflect the near real-time variations happening within the process.