Integrating Continuous-Time and Discrete-Event Concepts in Process Modelling, Simulation and Control

Currently, modelling of systems in the process industry requires the use of different specification languages for the specification of the discrete-event and continuous-time subsystems. In this way, models are restricted to individual subsystems of either a continuous-time or discrete-event nature. It is our aim to integrate such models, by using one language for the specification of complete plants or production units. For this purpose, we introduce the language Chi in this paper. This language integrates a small number of orthogonal continuous-time and discrete-event concepts. The continuous-time part of Chi is based on DAEs; the discrete-event part is based on a CSP-like concurrent programming language. Models are specified in a symbolic mathematical notation. A case study is presented of a plant for the biochemical production of ethanol. The production takes place in a number of fermentors in a fed-batch fashion. The fermentation process and the control system, which controls the various valves and pumps and schedules the different batches, are both specified in Chi.. The example illustrates the relevance of integrating continuous-time and discrete-event concepts