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 χ in this paper. This language integrates a small number of orthogonal continuous-time and discrete-event concepts. The continuous-time part of χ is based on DAEs; the discreteevent 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 χ . The example illustrates the relevance of integrating continuous-time and discrete-event concepts.