A new procedure for synthesizing process flow sheets and base-case designs has been developed. The procedure is evolutionary in nature and proceeds through a hierarchy of decision levels, where more fine structure is added to the flow sheet at each decision level. Heuristics are used to obtain some of the structural elements of the flow sheet, and other heuristics are used to make some of the decisions required at the various decision levels. In many cases, no heuristics are available, so that process alternatives are generated. The analysis protion of the procedure has strong focus on the economic tradeoffs that are associated with the significant design variables.