A knowledge-based system for the conceptual design of gas and liquid separation systems

Most recent research in the synthesis of separation systems has been focused on the development of more rigorous procedures for the design and synthesis of specific unit operations, rather than the synthesis of these units as a part of the overall flowsheet. Furthermore, many of the chemical process used in the production of commodity and specialty chemicals are characterized by many reaction steps with separations required between each step. The coupling of the reaction and separation steps has a significant impact on the recycle and separation system structures. A completely integrated hierarchical procedure has been developed for the conceptual design of vapor-liquid separation systems found in multiple reaction step processes. A new decomposition procedure is presented for determining the general structure of the separation system for processes involving reactions which occur in vapor-liquid-liquid-solid phase mixtures. The interactions of the separation subsystems for; vapor recovery, solid recovery, and liquid separations are identified, including process recycles between subsystems. The vapor recovery system and distillation sequence are then synthesized, the dominant process design variables are identified, the size and cost of the process units are determined, and the economic potential is calculated. Alternatives can then be quickly compared and ranked. Design procedures have been implemented in an expert system environment for the synthesis of gas membrane, condensation (high pressure or low temperature), and complex distillation columns (sidestream, side rectifier, and side stripper columns) separations. Finally, a procedure is presented for assessing the incentive for the combining of distillation systems in multiple step reaction processes. Dilute mixture separations generally represent the highest separation costs in the distillation system. The pooling of plant distillation separations can lead to better separations by reducing flow imbalances and dilute mixtures in the separation system feed. A hybrid of object-oriented and rule-based techniques has been used in the development and implementation of the procedure in PIPII, a computer-aided design tool which can rapidly generate process flowsheet alternatives and estimate the optimum range of the process conditions. The hierarchical nature of the procedure quickly prunes the number of viable alternatives which must be examined for a given process. The procedures, reasoning, and methods are thoroughly discussed within