Model simplification and time-scale assumptions applied to distillation modelling

A generic industrial plant (or section of plant) can be abstracted as a set of capacities exchanging extensive quantities through connecting streams. This abstraction is applicable with different granularities, focusing on smaller or bigger control volumes according on how well the dynamics of the process must be studied. The studied system can be represented as a directed graph, where the capacities are the nodes and the streams are the arcs. The graph of the plant (or of the single operation unit) is a schematisation of the process; the model can then be written as a system of differential and algebraic equations to be solved with a numerical solver. Here we discuss how one can simplify a detailed distillation model. In the studied detailed distillation model, each distillation stage is a dynamic rate-based flash. A cascade of simplified models is accomplished by a systematic procedure that combines singular perturbation and lumping.