A blackboard-based expert system, Intellite 3 for synthesizing control structures in chemical processing plants is discussed. We suggest object-centered knowledge representation framework with distributed multi-task frame net model embodied on blackboard structure. Intellite 3 interactively synthesizes the plausible control structures for a specified process and it effectively screens those alternatives to find out the most reasonable one in the context of over-all control objectives, operability, and other operational requirements.