This work describes an expert system for synthesis and design of control systems for chemical processing plants. We also outline the knowledge representation schemes for the expert system with object oriented programming concepts on control system design, control objectives and their relationships to the knowledge structure shaped in this study-Task Frame Net Model. Based upon various control objectives, shortcut calculations, and several heuristics including control idioms. Intellite³-the expert system developed in this study-synthesizes interactively the plausible control structures for a specified distillation column and screens effectively those alternatives to find out the most reasonable one in the context of overall control objectives, operability, and other operational requirements.